IP Routing on z/OS

© 2014 IBM Corporation
IP Routing on z/OS
Mike Fox, Software Architect
IBM Enterprise Networking Solutions
mjfox@us.ibm.com

© 2014 IBM Corporation© 2014 IBM Corporation2
Ÿ Basic IP routing concepts

Ÿ ARP, Default routing, Nets, subnets, supernets, forwarding,
IPv6

Ÿ Basic z/OS routing concepts

Ÿ IP routing table

Ÿ Deﬁning static routes

Ÿ Layer 2 routing (including ARP takeover)

Ÿ Dynamic routing concepts

Ÿ OSPF, RIP, “connection” routing

Ÿ Dynamic routing on z/OS

Ÿ OMPROUTE structure,

Ÿ Conﬁguring

Ÿ Monitoring

Agenda

Basic IP routing concepts

TCP/IP Addressing – IPv4
§ IPv4 uses four byte addressing structure e.g., 198.51.100.36

Ø Broken into netID and hostID portion

Ø The mask indicates which part is network and which part is host

Ø Expresses as a mask (e.g., 255.255.255.0) or a number of mask bits (e.g., /24)

§ The “class mask” is the network mask that goes with an address class

§ Class A mask: 255.0.0.0 or /8

§ Class B mask: 255.255.0.0 or /16

§ Class C mask: 255.255.255.0 or /24

0
Class A:

10
110
8
1
6
2
4
3
1
netID
netID
netID
hostID
hostID
hostID
Class B:

Class C:

TCP/IP Addressing nets, subnets, supernets
§ Network address: mask is equal to the class mask

§ E.g., 9.0.0.0/8

§ Subnet address: mask is longer than the class mask, meaning the standard host portion
has been “subnetted”

§ E.g., 9.1.1.0/24

§ Supernet address: mask is shorter than the class mask, meaning multiple networks are
being addressed

§ E.g., 192.168.0.0/16

§ Host address: mask is all 1’s. Addresses a single host on the network.

§ E.g., 192.168.1.1/32

§ Networks, subnets, and supernets are key to IPv4 routing

§ By collapsing multiple addresses into nets, subnets, and supernets, we reduce the size
of the routing tables

§ E.g., a route to 9.0.0.0/8 reaches every IP address in the 9.0.0.0 network (9.x.x.x)
rather than having to specify a host route to every destination

Special addresses
§ With supernetting and subnetting the mask can be anything and network classes are less
meaningful.This is called Classless Inter Domain Routing (CIDR) and the mask is usually
called a subnet mask no matter its actual class.Almost all modern networks use CIDR.
Henceforth we will use the term subnet mask for all IPv4 masks.

§ Every subnet has two special reserved addresses

§ The subnet broadcast address: all host bits are 1’s

§ The subnet number: all host bits are 0’s

§ Example: 192.168.255.255 is the broadcast address and 192.168.0.0 is the subnet
number for subnet 192.168.0.0/24.
§ These addresses should NOT be assigned to hosts
§ Result: the longest practical subnet mask in IPv4 is /30, or 255.255.255.252.
A subnet this size has a subnet number, a subnet broadcast address, and two
hosts.
§ Example: subnet 192.168.1.4/30

§ 192.168.1.4: subnet number

§ 192.168.1.5: host

• 192.168.1.6: host
• 192.168.1.7: broadcast address

§ IPv6 is an evolution of the “current” version of IP, which is known as IPv4

§ Expanded Routing and Addressing

§ Address space increased from 32 bits to 128 bits

§ IPv6 addresses are written as hexadecimal half-words separated by colons

§ One set of consecutive half-words of zeroes can be omitted and replaced with ::

TCP/IP addressing – IPv6
2001:0db8:4545:0:0:09ff:fef7:62dc

2001:0db8:4545::09ff:fef7:62dc

(these are the same address with the zeroes replaced with :: in the
second example

Important difference: in IPv6 an interface can have
multiple IP addresses and they usually do

§ In IPv6 the concept of subnetting is replaced with prefix

§ There are no address classes, and prefix lengths are always variable (but
usually 64 bits)

§ Prefix notation is always significant bits

IPv6 prefixes
2001:0db8:4545::/64

(specifies a 64 bit long prefix)

2001:0db8:4545::09ff:fef7:62dc/128
(specifies a host prefix)

§ Like IPv4, a prefix route addresses all addresses that fall within that prefix

§ Unlike IPv4 there is no broadcast address for a prefix so the all 1’s address
can be assigned to a host

§ IPv6 supports multicast but not broadcast.

IPv6 scopes
§ Unlike IPv4, IPv6 address have scope. An IPv6 address is only unique within its
scope. Most commonly used scopes are:

§ Link local (all addresses in prefix fe80::/10)

§ Only unique on a specific link (e.g., ethernet LAN segment)

§ Every non-VIPA interface must have a link-local address

§ Global (all addresses in prefix 2000::/3)

§ Can be addressed from anywhere

§ For comparison, all IPv4 addresses are global

§ Some quick math reveals that the IPv6 global address space is HUGE

§ Usually, a physical interface has both a global and a link-local address

§ AVIPA only has a global address

IPv6 Link Local scope illustrated

ARP – mapping an IPv4 address to a MAC address
§ Address Resolution Protocol (ARP) is used to map an IPv4 address to the MAC
address of an adapter on the link

§ The most basic form of routing, it underlies all other routing

§ A stack queries the LAN to ﬁnd the MAC for an IP address

§ The owner responds and the result is cached in the ARP cache

Destination
Host
Sending
Host
Other
Host
Adapter IP:
9.1.1.1
Adapter IP:
9.1.1.2
Adapter IP:
9.1.1.3
MAC A
MAC B
MAC C
I have 9.1.1.2, and the
MAC addr is MAC B
Who has 9.1.1.2?
1
2

ARP – gratuitous ARP
§ A host can send a gratuitous ARP to proactively notify neighbors on the LAN that
it has an IP address. This is commonly done.

§ Lets the rest of the network know where an address is without having to ask
and cache at send time

§ Improves performance, fewer wasted ﬂows

Destination
Host
Sending
Host
Other
Host
Adapter IP:
9.1.1.1
Adapter IP:
9.1.1.2
Adapter IP:
9.1.1.3
MAC A
MAC B
MAC C
Hey guys,FYI,
9.1.1.1 is at
MAC A!

NeD – mapping an IPv6 address to a MAC address
§ Instead of ARP, IPv6 uses Neighbor Discovery

§ Neighbor Discovery is similar to ARP but has improvements

§ More proactive notiﬁcation and robustness and supports IPv6
enhancements like autoconﬁguration of IP addresses

§ The Neighbor Discovery (ND) cache replaces the ARP cache

IPv6 Stateless Autoconfiguration
§ Stateless autoconfiguration is a powerful capability of IPv6

§ IPv6 addresses can be automatically assigned to interfaces!

§ Significantly enhances flexibility and mobility of IPv6 networks

§ Requires use of 64 bit prefix length

§ Method: 64 bit Link prefix is prepended to the 64 bit interface ID

§ Link prefix automatically learned from router (part of NeD)

§ Interface ID can be configured or automatically derived from the
link’s MAC address

§ Link local address is always created this way (fe80::+interface ID)

§ Advantages:

§ If a host moves, it can learn the prefix of the new link and
automatically reconfigure its interface IP addresses (great for mobile
devices or any other host relocation scenario)

§ Router can better control addressing on its link

IPv6 Stateless Autoconfiguration illustrated
Host
Interface MAC: 0B:32:45:67:89:AA
Router
Router solicitation
“I’m new here, what’s the config?”
Router advertisement
“The link prefix is 2001:0db8:1:1::/64 and the default router is at fe80::3000:1::1”
Resulting interface configuration:
Link local addresss: fe80::0b32:45ff:fe67:89aa (always configured this way)
Global IP address: 2001:0db6:1:1:: 0b32:45ff:fe67:89aa (from the router advertisement)
Link local addr:
Fe80::3000:1::1

Basic z/OS routing concepts

IP Routing Table
§ The z/OS Comm Server TCP/IP stack uses an IP routing table to route
packets

§ You can display it with NETSTAT ROUTE

MVS TCP/IP NETSTAT CS V2R1 TCPIP Name: TCPCS 14:24:09
IPv4 Destinations
Destination Gateway Flags Refcnt Interface
----------- ------- ----- ------ ---------
Default 9.67.115.65 UGS 0000000002 OSAQDIOLINK
9.67.115.0/24 9.67.115.72 UGS 0000000000 OSAQDIOLINK
9.67.115.69/32 9.67.115.72 UGHS 0000000000 OSAQDIOLINK
9.67.112.0/24 0.0.0.0 US 0000000000 OSAQDIOLINK
To reach this destination go out this IP interface
to this next hop address
1
2
3
4
Direct route (no next hop required)

Notes on the routing table
§ TCP/IP uses the “most speciﬁc match” method of picking a route for a
destination.

§ If a host route (for example, route 3 on the previous slide) for the
destination exists, use it

§ If not, use the most speciﬁc (longest mask) subnet route that matches

§ If no match found, use the default route (for example route 1 on the
previous slide)

Example route destination Route used on the previous slide
9.67.115.69 3 (matching host route)
9.67.115.32 2 (most specific subnet route)
9.1.1.1 1 (default route)
9.67.112.1 4 (most specific subnet route)

Route Flags
§ The Flags field gives good information about routes. The most common values are:

§ U: the route is up and available for use

§ S,Z: static route (coded into the TCP/IP profile, more on this later)

§ O,R,C: Route learned from OMPROUTE (more on this later)

§ G: Route uses a gateway (not a direct route)

§ H: Route is a host route

§ More flags are documented in IP Sysadmin Commands

§ The RefCnt tells you how many connections are currently using the route

IPv4 Destinations
----------- ------- ----- ------ ---------
9.67.115.0/24 9.67.115.72 UGS 0000000000 OSAQDIOLINK

Multipath
§ Multiple routes to the same destination are supported;This is called “multipath”

§ How it’s handled depends on conﬁguration of IPCONFIG MULTIPATH

§ NONE: ﬁrst matching route is always used

§ PERCONNECTION: Each connection is assigned to a route in a round-robin
fashion (recommended, provides load balancing)

§ PERPACKET: Each packet is assigned to a route in a round-robin fashion (not
recommended, can cause reordering problems within connections)

IPv4 Destinations
----------- ------- ----- ------ ---------
9.67.115.0/24 9.67.115.72 UGS 0000000000 OSAQDIOLINK
2 multipath routes to 9.67.115.69 using 2 different next hop routers

A note about IPv6 routes
§ Everything said here also applies to IPv6 routes but IPv4 routes are used in the examples
in the interest of space

§ Because of the length of IPv6 addresses, IPv6 routes are displayed after IPv4 routes in
Netstat reports, and in a different format that doesn’t ﬁt well on slides.

IPv6 Destinations
DestIP: Default
Gw: 2001:0db8::206:2aff:fe71:4400
Intf: OSAQDIO46 Refcnt: 0000000000
Flgs: UGS MTU: 1492
DestIP: 2001:0db8::9:67:115:13/128
Gw: ::
Flgs: UD MTU: 1492
DestIP: 2001:0db8::206:2aff:fe71:4400/128
Gw: ::
Flgs: UHS MTU: 1492

Static Routes
§ Static routes are defined in the TCP/IP profile (as opposed to learned from the network).
There are two types of static routes in z/OS:

§ REPLACEABLE: If a dynamic route is learned to the same destination, the dynamic
route replaces the static route. If the dynamic route is lost, the static route is restored.

§ Consider these “last resort, backup” routes to be used when dynamic routing
fails to find a destination.

§ The Netstat flag for these routes is “Z”

§ NONREPLACEABLE:This route cannot be replaced by a dynamically learned
route.This is a “must use” route that overrides all dynamics.

§ Even if this route is unavailable (for example uses a router or interface that is
down) and dynamic routing learns a route that is available, this route will be used
(i.e., the destination will be unreachable).

§ The Netstat flag for these routes is “S”

§ Static routes are easier and simpler, but they do not provide any automatic rerouting
around failures or network changes.

§ If the network topology changes, either planned or because of outages, the static
routes must be reconfigured

Defining static routes
§ In z/OS Communications Server, static routes for both IPv4 and IPv6 are defined using the
BEGINROUTES definition block in the TCP/IP profile

BEGINRoutes
;
; Destination/Mask First Hop Link Name Pkt Size Opts
;
DEFAULT 130.50.75.1 OSAQDIOLN1 MTU 2000
ROUTE 130.50.75.0/24 = OSAQDIOLN1 MTU 2000
ROUTE 193.5.2.0/24 = OSAQDIOLN2 MTU 1500
ROUTE 193.7.2.2/32 = MPCCTCLNK1 MTU 2000
ROUTE 12.17.99.0/24 130.50.75.1 OSAQDIOLN1 MTU 2000 REPL
;
DEFAULT6 fe80::230:71ff:fed3:5160 OSAQDIO61 MTU 3000
ROUTE 2001:0DB8::/64 = OSAQDIO61 MTU 3000
ROUTE 2001:0DB8::1:1/128 fe80::230:71ff:fed3:5160 OSAQDIO62 MTU 1500
;
ENDRoutes
This route is replaceableFirst hop of = means direct route

Modifying Static Routes
§ To modify static routes, a new BEGINROUTES block must be coded and
added to the profile usingVARY OBEYFILE

§ VARY OBEYFILE is the command that applies changes to the TCP/IP
profile

§ A new BEGINROUTES block is a complete replacement, so the
entire static route table must be replaced to make a change

§ Only one BEGINROUTES block is allowed in a TCP/IP profile. If
there are multiple blocks the last one will replace any previous
ones.

§ The single BEGINROUTES block contains both IPv4 and IPv6
static routes.

§ Example: If you doVARY OBEYFILE to add IPv6 static
routes, you have to include the existing IPv4 static routes
that you want to keep as well or they will be deleted

Why use Static Routes?
§ Static routing is most useful in a simple, stable network configuration

§ For example if z/OS is not in a sysplex and is on a LAN with a router that takes
responsibility for routing all hosts on the LAN

§ A static default route pointing to the router and a static subnet route for the
attached LAN may be sufficient

§ But remember, hosts in the network still have to be able to reach you!

§ So without dynamic routing to advertise your destinations, static routes will also
have to be coded on the router and other hosts on the LAN to reach your host,
unless you’re using a flat layer 2 network configuration (more on the next slide)

§ A static route configuration can be simpler and use less CPU (no routing daemon
running).

§ But with limited resilience. In the example above, if the router goes down and a
backup router takes over, static routes will have to be modified to maintain
connectivity

TN3270e
Server
VIPA#1
CICS Appl-A
VIPA#2
FTP
Services
VIPA#3 DB2
subsystem
VIPA#4
OSA OSAOSA
CICS Appl-B
VIPA#5
Web Services
VIPA#6
IP#10 IP#11 IP#12
Connect to VIPA#1
Connect to CICS-Appl-
A.xyz.com
My z/OS IP host
Resolve CICS-Appl-
A.xyz.com
Use IP address VIPA#2
Name
server
A VIPA is an IP
address that is not
tied to a specific
physical interface
and instead
represents a higher
level concept such as
a host, an
application, or a load
balancer.
VIPA#7
Flat Layer 2 network: first, an introduction to VIPA

What is a Flat Layer 2 network?
§ In a flat layer 2 network configuration, VIPAs on a host are defined to be in the
same subnet as an attached physical LAN/VLAN

§ Disadvantage: limitsVIPA flexibility and tiesVIPAs to a specific LAN (to which
there can be multiple interfaces attached)

§ Advantage: improves robustness in static routing configurations

§ The key to a flat layer 2 network is that z/OS Communications Server
registers all VIPAs that are in the same subnet as an OSA
interface, to that OSA interface

§ The OSA interface then

§ performs ARP on behalf of the registeredVIPAs, and

§ forwards packets to registeredVIPAs up to the TCP/IP stack

§ This is a unique z/OS + OSA value added function

z/OS VIPA address visibility on a flat layer 2 network
§  OSA interfaces will do gratuitous ARP for the
OSA interface IP address and for VIPA
addresses that belong to the same subnet as
the OSA interface.
§  Note that VIPA 10.1.2.1 in TCPIPB is not eligible
for this optimization because it’s not in the OSA
subnet
OSA OSA
Port name PORTA
Home IP address 10.1.1.1
Mac address MAC1
Port name PORTB
Mac address MAC2
TCPIPA
VIPA 10.1.1.10
OSA OSA
Port name PORTC
Mac address MAC3
Port name PORTD
Mac address MAC4
TCPIPB
VIPA 10.1.2.1
XCF IP address:
10.1.3.1
XCF IP address:
10.1.3.2
Host-2: 10.1.1.6
IP Address MAC Address
10.1.1.1 MAC1
10.1.1.2 MAC2
10.1.1.3 MAC3
10.1.1.4 MAC4
10.1.1.10 MAC1
Router’s ARP cache
Gratuitous ARP
and respond to
ARP requests for:
•  10.1.1.1
•  10.1.1.10
Gratuitous ARP
and respond to
ARP requests for:
•  10.1.1.4
IP Address ARP Owner
10.1.1.1 Yes
10.1.1.10 Yes
10.1.1.2 No
10.1.3.1 No
OSA PORTA’s Address Table
IPv4 subnet: 10.1.1.0/24
Router: 10.1.1.5

10.1.1.1 MAC1
10.1.1.2 MAC2
10.1.1.10 MAC1
10.1.1.3 MAC3
10.1.1.4 MAC4
VIPA movement on a flat network (without dynamic routing)
OSA OSA
Port name PORTA
Mac address MAC1
Port name PORTB
Mac address MAC2
TCPIPA
VIPA 10.1.1.10
OSA OSA
Port name PORTC
Mac address MAC3
Port name PORTD
Mac address MAC4
TCPIPB
VIPA 10.1.2.1
XCF IP address:
10.1.3.1
XCF IP address:
10.1.3.2
Router: 10.1.1.5 Host2: 10.1.1.6
IPv4 subnet: 10.1.1.0/24
10.1.1.1 Yes
10.1.1.10 Yes
10.1.1.2 No
10.1.3.1 No
10.1.1.1 MAC1
10.1.1.2 MAC2
10.1.1.10 MAC3
10.1.1.3 MAC3
10.1.1.4 MAC4
10.1.1.3 Yes
10.1.1.10 Yes
10.1.1.4 No
10.1.3.2 No
10.1.2.1 No
OSA PORTC’s Address Table
Moving VIPA 10.1.1.10 to another LPAR
When 10.1.1.10 is added to OSA PORTC’s OAT with ARP ownership, PORTC sends out a gratuitous ARP that forces nodes on the
LAN with that IP address in their ARP cache to update their ARP cache entry with the new MAC address.
Grat ARP for
10.1.1.10
10.1.1.1 Yes
10.1.1.10 Yes
10.1.1.2 No
10.1.3.1 No
VIPA 10.1.1.10

ARP Takeover:
Additional layer 2 resilience provided by z/OS+OSA
§ ARP takeover is an additional z/OS + OSA function to keep networks resilient,
without dynamic routing

§ When a z/OS TCP/IP stack has multiple OSA interfaces on the same subnet:

§ The interfaces learn about each other

§ They form a “LAN Group.”

§ The interfaces back each other up seamlessly and automatically

§ If one goes down, the other(s) take over ARP responsibility for the
addresses the failed interface owned

§ Result: Seamless failover between OSA interfaces in case of failures

§ Illustrated on the following slides.

ARP Takeover Illustrated
OSA OSA
Port name PORTA
Mac address MAC1
Port name PORTB
Mac address MAC2
TCPIPA
VIPA 10.1.1.10
Router: 10.1.1.5/24
10.1.1.1 Yes
10.1.1.10 Yes
10.1.1.2 No
10.1.3.1 No
10.1.1.1 No
10.1.1.10 No
10.1.1.2 Yes
10.1.3.1 No
OSA PORTB’s Address Table
10.1.1.1 Yes
10.1.1.10 Yes
10.1.1.2 No
10.1.3.1 No
10.1.1.1 Yes
10.1.1.10 Yes
10.1.1.2 Yes
10.1.3.1 No
OSA PORTB’s Address Table
XCF IP address:
10.1.3.1
10.1.1.1 MAC1
10.1.1.2 MAC2
10.1.1.10 MAC1
10.1.1.1 MAC2
10.1.1.2 MAC2
10.1.1.10 MAC2
OSA PORTA fails
When PORTA fails, PORTB
is takes over ARP ownership
of the addresses PORTA
previously had. PORTB
sends gratuitous ARPs to
enable downstream hosts to
update their ARP cache.
z/OS TCP/IP supports
interface recovery if
multiple network
interfaces to the same
subnet exist.
In this example, both
OSA PORTA and PORTB
are connected to the
10.1.1.0/24 subnet.

Monitoring LAN groups and ARP takeover
§  Messages are issued when an interface takes over ARP responsibility
– EZD0040I INTERFACE OSAQDIO2 HAS TAKEN OVER ARP RESPONSIBILITY FOR
INACTIVE INTERFACE OSAQDIO1
§  Messages are issued whenever a previously taken over link or interface recovers and takes
back the ARP responsibility.
– EZD0041I INTERFACE OSAQDIO1 HAS TAKEN BACK ARP RESPONSIBILITY FROM
INTERFACE OSAQDIO2
§  Use Netstat DEvlinks/-d report to tracks the state of takeover:
– Displays ARP/ND information.
– LAN group membership is determined dynamically per interface during interface
initialization
– LAN group numbers are determined dynamically, they are not configured
.........
IPv4 LAN Group Summary
LanGroup: 00010
Name Status ArpOwner VipaOwner
---- ------ -------- ---------
O3OSXA0 Active O3OSXA0 Yes
IPv6 LAN Group Summary
LanGroup: 00001
Name Status NDOwner VipaOwner
---- ------ ------- ---------
EZ6OSM02 Active EZ6OSM02 Yes
EZ6OSM01 Active EZ6OSM01 No

The fine print! (Some of the rules for availability and DVIPA
movement in flat networks without dynamic routing)
§  z/OS VIPA addresses in a flat network configuration without dynamic routing must be
allocated out of the same subnet as the directly attached network - in this example, the
10.1.1.0/24 subnet.
– If multiple VLANs are used on the network, VIPA addresses belonging to one VLAN
(one subnet) can in general only be accessed and recovered via that VLAN
– A default router that does know about all DVIPAs, can be used to reach VIPAs on
other VLANs (subnets)
§  All LPARS in the Sysplex must be attached to one and the same IP subnet via OSA
ports.
§  Network interfaces belonging to other IP subnets cannot be used for automatic re-
routing around failed OSA ports.
– That includes MPC links, XCF links, or other OSA-attached subnets
§  Overall physical availability of the network to which the OSA ports are attached
becomes of outmost importance and must generally be based on what is known as
Layer2-and-below availability functions in the switches and the physical links (cables).
– Redundant switches with trunk links – part of the zEnterprise infrastructure
– Redundant OSA adapters in each LPAR – always use at least two OSX ports
– OSA port cabling to multiple switches – part of the zEnterprise infrastructure

Basic Dynamic Routing
Concepts

Dynamic routing protocols supported on z/OS
§ z/OS Communication Server supports three dynamic routing protocols

§ Connection routing: a relatively trivial method of determining
reachability of directly attached subnets.

§ (Maybe should say we support 2 ½ dynamic routing protocols)

§ Routing Information Protocol (RIP): A relatively simple distance
vector protocol

§ Distance vector means: based on routers sharing their routing tables
with each other

§ Open Shortest Path First (OSPF): The primary and recommended
routing protocol for z/OS. It’s a link state protocol

§ Link state means: based on routers learning the network topology from
each other, then each one independently calculating its routing table based
on learned topology

All protocols are supported for both IPv4 and IPv6
and are implemented by the OMPROUTE daemon

Connection Routing
§ When an interface becomes available, its attached subnet becomes a reachable
destination

§ Learned simply by virtue of an interface coming up, no communication with
other routers or hosts required.

§ Connection routes are indicated by the “C” ﬂag in Netstat reports

z/OS Host
Interface OSA1:
9.1.1.1/24
Subnet 9.1.1.0
IPv4 Destinations
----------- ------- ----- ------ ---------
9.1.1.0/24 0.0.0.0 UC 0000000000 OSA1
9.1.1.1/32 0.0.0.0 UH 0000000000 OSA1
OMPROUTE
“Implicit route” is
always added by the
stack for each local
interface IP address
“Connection
route” to the
interface’s
subnet is added
by OMPROUTE

When is connection routing useful?
§ If z/OS is using dynamic routing and is attached to a back-end network that uses
a ﬂat layer 2 conﬁguration

§ That is, every IP address on that back-end network is in the same subnet

§ Meaning that a route to the subnet can reach every host on the back-end
network (via ARP routing), for example

§ A back-end LAN with one or more blade centers attached and the
blades are all single homed and withoutVIPAs

§ Single-homed means they only have IP interface onto the network

§ zEnterprise IEDN

§ It’s almost always used in conjuction with OSPF or RIP running on other
interfaces attached to more complex networks.

RIP: Routing Information Protocol
§ RIP is based on routers sharing their routing tables with each other

§ Each router tells its neighbors what destinations it can reach, routers add their
hops and then inform their neighbors

9.1.1.1
9.1.1.2
9.1.2.2
9.1.2.3
9.1.3.3
9.1.3.4
I’m 9.1.1.1 I’m 9.1.2.2
And 9.1.1.1 is one hop away from
me and 9.1.1.2 is zero hops away
from me
I’m 9.1.3.3
And 9.1.1.1 is two hops away from me
and 9.1.1.2 and 9.1.2.2 are one hop
away from me amd 9.1.2.3 is zero hops
away from me.
Destination Distance
9.1.1.1 1
9.1.1.1 2
9.1.1.2
9.1.2.2
1
1
9.1.1.1 3
9.1.1.2
9.1.2.2
2
2
9.1.2.3
9.1.3.3
1
1
Resulting
route
tables on
each host

More on RIP
§ The illustration on the previous slide is obviously a simplification of RIP but
shows how distance vector algorithms work

§ RIP can use subnet routes, it doesn’t have to show the distance to every
host route

§ RIP has algorithms to prevent routing loops

§ The distance value defaults to 1 per hop but interfaces can be configured
to have higher distance values

§ In RIP, complete routing tables are sent out every 30 seconds

§ A route not updated within the last 180 seconds is considered
unreachable

§ If there are topology changes, they can be sent out sooner

§ RIP routes timeout if not refreshed within the last 180 seconds

§ The maximum distance allowed in RIP is 15. A distance of 16 means
“infinity” (unreachable)

§ There are both IPv4 and IPv6 versions of RIP but they work essentially the
same way.

RIP pros and cons
§ PROs

§ Simplicity

§ Uses less CPU because no route calculations are being done

§ CONs

§ Limited network size supported (since distance of 16 = inﬁnity)

§ Can use a lot of network bandwidth (since entire routing tables are sent
every 30 seconds)

§ Slow to respond to outages (180 second timer to invalidate a route)

§ Multipath is not supported

§ In other words, can only learn one route to a speciﬁc destination

OSPF: Open Shortest Path First
§ Unlike RIP, OSPF is a link state protocol

§ This means that routers exchange topology information, not routes, and
each one uses that info to compute its own route table

§ This exchange of topology makes the protocol more powerful and complex than
RIP, because of questions like:

§ How does a router know who to exchange topology with?

§ How much of the network topology does any one router have to know?

§ How is topology represented?

§ How is the routing table built?

§ A full OSPF tutorial would ﬁll a presentation on its own so we will only cover
some basic high level concepts.

OSPF: How does a router know who to exchange
topology with?
§ Routers use the hello protocol and adjacencies to track each other

§ The hello protocol is both a probe and a keepalive

§ Routers multicast hello packets to all other routers every hello
interval (z/OS default 10 seconds), using a special OSPF multicast
address

§ Routers not heard from for the dead router interval by their
neighbors are considered down and unreachacle (z/OS default 40
seconds)

§ The adjacency is how routers keep track of their immediate neighbors

§ Routers fully communicating with each other and exchanging
topology are fully adjacent (neighbor state 128)

§ Routers go through a progression of states to negotiate and mange
adjacencies. Not all physically connected routers become fully
adjacent with each other.

Hello and adjacency illustrated

OSPF: What is the designated router?
§ If there are multiple routers on a LAN, fully meshed adjacencies would be a large
processing burden. So for efficiency, one router on a LAN is elected the
“Designated Router” (DR) and another becomes the Backup Designated Router
(BDR)

§ DR and BDR become fully adjacent with every other router on the LAN

§ The non-DR LAN members only become fully adjacent with the DR and the
BDR, not with each other (their neighbor states stop progressing at “2way”)

§ In this manner, the DR “owns” the LAN for OSPF purposes

§ Gathers topology info from all members and advertises it to the rest of
the network

§ Receives topology info from the rest of the network and distributes it to
the other LAN members

§ The BDR quietly waits to take over if the DR fails

§ The “Designated Router Priority” guides the negotiation to pick the DR and
BDR so admins have significant influence here

§ Tip: the DR and BDR should be real routers (e.g., Cisco boxes) not a
data host (e.g., z/OS host) whenever possible

Designated Router Illustrated
Host 1
Host 2
Host 3
Router
(DR)
Router
(BDR)
IF IF IF
Full adjacency (state 128) with topology exchange
Two-way adjacency (state 8) with hello keepalive only
Notes:
Ø BDR is optional
Ø As the number of non-DR
hosts increases, the efficiency
benefit increases
To the rest of the network

How much of the network topology does any one
router have to know?
§ To prevent every host in the OSPF domain from being overwhelmed with WAN
topology, the OSPF domain is divided into areas.

§ Routers only exchange and store topology for their speciﬁc area

§ Destinations outside the area are reached using area-border routers and
summary routes

§ Areas are named using 32 bit numbers written in dotted decimal notation
(including in IPv6), for example area 1 is 0.0.0.1

§ The backbone area (area 0.0.0.0) is a special area… all other areas must be
attached to it and all inter-area routing must go through the backbone.

§ The backbone area is, as the name implies, the backbone of the OSPF domain

§ Two non-backbone areas cannot be directly connected… must go through
the backbone

§ Stub areas and totally stubby areas are another special type of area that limit the
amount of information that hosts within the area have to learn about the rest of
the network

Backbone area, illustrated
• Routers Rb, Rc and Rf are Area Border Routers (ABRs)
• They manage the exchange of data between areas and maintain topology
databases for both areas they belong to.
• Routers Ra, Rd, Re, Rg, Rh, and Rk only maintain topology for their respective areas
and they learn about inter-area routes from the Area Border Routers that attach their
areas to other areas.

Totally stubby areas
§ Routers learn about destinations in other areas from summary routes advertised
by the area-border routers.

§ In a large network this can be a large number of routes

§ Totally Stubby Areas are special areas that limit the amount of inter-area
topology that the routers and hosts have to know.Area 4.4.4.4 on the previous
slide is a totally stubby area.

§ Instead of advertising inter-area destinations into a stub area, a totally stubby
area border router simply advertises a default route into the stub area
(destinations within the totally stub area are still advertised to the backbone)

§ It’s in effect saying “don’t worry about what’s outside this area, just
forward all packets to me and I’ll handle it”

§ This greatly reduces the size and complexity of routing tables within a totally
stubby area

§ For this reason it’s recommended to place z/OS hosts and sysplexes
within totally stubby areas whenever possible

§ Restriction: a totally stubby area only works if all the area border routers
that it uses can actually reach all destinations outside the area

§ Good network design should ensure this.

Autonomous systems and external routes
§ A routing domain is also called an Autonomous System (AS). One Autonomous
system uses one routing protocol. Examples of Autonomous Systems:

§ A corporation’s OSPF network

§ The same corporation’s RIP network

§ The same corporation’s static network (i.e., areas where no routing
protocol is running)

§ A router that acts as a boundary between AS’s is called an Autonomous System
Boundary Router or ASBR.

§ An ASBR’s job is to manage the import and advertisement of routes
between different AS’s. For example, importing RIP routes into OSPF and
vice versa

§ z/OS supports being an ASBR, but even if you’re not an ASBR, it’s important
to understand what an external route is

§ An external route is a route imported into the AS from another AS. For
example, a destination that is reached via a static or RIP route that’s
advertised into OSPF is an AS external destination

Areas and AS’s: putting it all together
• This picture shows two AS’s (the OSPF AS and the attached RIP AS) and three areas
(the OSPF backbone area, a non-backbone area, and a Totally Stubby area).
• Router 3 is an ASBR and an ABR. It imports destinations from the RIP AS into
OSPF. It also manages the boundary between the backbone and the totally stubby
area
• Router2 is an ABR. It manages the boundary between the backbone area and the
non backbone area.

Flooding: getting the topology info out there
• The previous picture showed which hosts originate what types of routing information.
To get routing information known beyond immediate neighbors, information is flooded
throughout the AS. Flooding means reforwarding received topology information
• This slide shows what type of information each router floods (reforwards). It’s important
to note that Router3 only floods a default route into the totally stubby area… sparing the
hosts therein from having to keep all the backbone, RIP, and non-backbone destinations
in their routing tables.

Building the routing trees
• As a result of flooding, each router learns the full topology of the area it belongs to.
• It uses this topology to use the Djikstra algorithm to calculate a routing tree
• This tree represents the best way to reach each destination in the area
• An ABR computes a separate tree for each area it’s attached to
• After the area trees are computed, the best route to reach each area destination, the
external (from other AS) routes, and summary (from other areas) routes are added to the
routing table.

Some notes on OSPF route computation
§ To reduce the number of entries in routing tables, OSPF computes subnet routes
whenever possible.

§ For example, to an IPv4 LAN only a subnet route will be added to the
routing table. There is no need to add host routes for the host interfaces on
that LAN, because they will all be in the LAN subnet so an individual host can
be found using ARP, once a route has gotten the packet to the LAN

§ This also applies toVIPAs, but you have to be more careful. If multipleVIPAs
in the same subnet are on different hosts, host routes will have to be
advertised instead of subnet routes. More on this on a later slide.

§ Because IPv6 has more flexibility in assigning IP addresses and prefixes than
IPv4, this isn’t always possible so in an IPv6 network you may find many more
host routes in a routing table.

§ For IPv6, the next hop in a computed route is always the link local address of the
next hop router’s interface on the LAN. Global addresses are never computed
as next hop destinations.

IPv4 OSPF vs. IPv6 OSPF
§ IPv4 OSPF is OSPF version 2

§ All routers and links are represented by their IP addresses

§ One of the IP addresses on a router is chosen to represent the router
(“Router ID”)

§ z/OS recommendation: use a staticVIPA

§ IPv6 OSPF is OSPF version 3

§ All routers and links are represented abstractly

§ Routers: by router ID, which is a 32 bit number represented in IPv4 style
dotted-decimal notation but is actually an arbitrary value

§ Links: represented by Interface ID, which is also an arbitrary 32 bit
number but is represented as an integer

§ Actual IP addresses are advertised separately from topology, referencing
topology (e.g., “the IP address of link 23 on router 1.1.1.1 is
2001:0db8::9:7”)

§ Building the routing table in IPv4: build the tree to ﬁnd the best route to each IP
address

§ Building the routing table in IPv6: build the tree to ﬁnd the best route to each
abstract topology element, then overlay the separately advertised IP addresses
on that tree to create the routing table.

OSPF pros and cons
§ PROs

§ Significant network design flexibility

§ Virtually unlimited network size and complexity supported

§ After initial synchronization, topology information is only flooded when it
changes, so uses less network bandwidth than RIP.

§ That’s a bit of a simplification but holds true. Each topology element is
also refreshed every 30 minutes if no changes

§ Responds to outages and topology changes quickly because it uses proactive
notifications and more timers, rather than relying on garbage collection like
RIP

§ Supports multipath (can compute multiple equal-cost routes to a single
destination)

§ CONs

§ Complexity

§ Because of route computations and keepalive timers, uses more CPU than
RIP.

So now you’re an expert on OSPF!?
§ OSPF is a complex and large protocol. We’ve only scratched the surface in this
presentation and we’ve done a lot of simplification in the interest of time

§ A full OSPF tutorial would be a presentation on its own

§ For more detailed information on OSPF you can consult:

§ RFC 2328

§ This RFC defines OSPF version 2 (for IPv4)

§ http://www.ietf.org/rfc/rfc2328.txt

§ RFC 2740

§ Defines OSPF version 3 (for IPv6)

§ Note this RFC assumes familiarity with OSPF version 2

§ http://tools.ietf.org/html/rfc2740

Dynamic Routing on z/OS

OMPROUTE
§ The OMPROUTE daemon performs
dynamic routing on z/OS

§ Open MultiProtocol Router

§ OMPROUTE implements OSPF and RIP,
for both IPv4 and IPv4.

§ It also does connection routing, and
integrates static routes from the TCP/IP
stack into the the OSPF & RIP domains.

§ OMPROUTE learns local conﬁguration
from the TCP/IP stack over an
Informational Socket

§ OMPROUTE communicates with other
routers using the OSPF and RIP
protocols and uses the information
learned to build its internal routing table

§ and then uses IOCTL calls to build
and update the stack’s routing table
from its internal table.

Configuring OMPROUTE
§ OMPROUTE is a z/OS Unix daemon and runs in the z/OS Unix shell

§ OMPROUTE locates its configuration file using the OMPROUTE_FILE
environment variable

§ Usually specified in the file pointed to by the STDENV card in the
OMPROUTE started PROC.

§ In the OMPROUTE configuration file, you specify:

§ General control information for each routing protocol being implemented

§ The dynamic routing characteristics of the stack’s IP interfaces

Sample OMPROUTE configuration file: OSPF
OSPF
Router_ID=10.138.165.9
;
Area
Area_number=1.1.1.1
Stub_area=yes
Import_Summaries=no
;
Area
Area_number=0.0.0.0
;
AS_Boundary_Routing
Import_Static_Routes=YES
Import_RIP_Routes=YES
;

Define the router ID (we recommend a
static VIPA)
This OMPROUTE is an area-border
router because it’s attached to two
areas:
§ Totally Stubby Area 1.1.1.1:
§ This router will advertise a
default route into 1.1.1.1 to
represent the backbone and the
rest of the network.
§ The backbone (0.0.0.0):
§ This router will advertise all
1.1.1.1 destinations into the
backbone as summary routes
This router is an AS Boundary router and will
import both Static and RIP routes into the
OSPF AS
ü Note that these routes will only be imported
into the backbone and non-stub areas. They
aren’t allowed in stub areas.

Sample OMPROUTE configuration file: IPv4 VIPA Interfaces
OSPF_Interface
IP_address=10.138.165.9
Name=SVIPA1
Subnet_mask=255.255.255.248
Attaches_to Area=1.1.1.1
Advertise_VIPA_ROUTES=HOST_ONLY
;
OSPF_Interface
IP_Address=10.138.200.160
Name=DVIPA
Subnet_mask=255.255.255.240
Attaches_to_area=1.1.1.1
;

IP Address and name must match the
stack’s definition
This is a special wildcard for dynamic
VIPAs. Note that the IP address is
actually the subnet number. Any
dynamic VIPA created that falls into
this subnet will use this definition if
no exact match was found.
For IPv4, the rules for matching a stack VIPA interface to an
OMPROUTE definition are:
1. If a static VIPA, match on the IP address then verify the name
matches the linkname
2. If a dynamic VIPA, do step 1 first, if no match then match on the
subnet number and the name is irrelevant
This is how you control whether
OSPF advertises a host or a subnet
route for the VIPA

Sample OMPROUTE configuration file: IPv4 OSA and
Hipersockets interfaces
OSPF_Interface
IP_address=10.72.116.14
Name=OSAQDIO1A
Subnet_mask=255.255.255.128
MTU=1500
Router_priority=0
Hello_interval=5
Dead_router_interval=20
Cost0=100;
OSPF_Interface
IP_Address=10.138.99.14
Name=HSOCKT12
Subnet_mask=255.255.255.240
MTU=8000
Router_priority=10
Cost=50
;

IP Address and name must match the
stack’s definition
Always specify the MTU or OMPROUTE
will use 576.
Router_priority of 0 means “I will not be
a designated router”
Always indicate which OSPF area an
interface is attached to
Because no routers can attach to
Hipersockets, someone has to be DR
The relatively lower cost indicates that the Hipersockets path is twice
as desirable as the OSA path, for route computation purposes

Sample OMPROUTE configuration file: wildcard interfaces
OSPF_Interface
IP_address=10.72.*.*
Subnet_mask=255.255.255.128
MTU=1500
Router_priority=0
Hello_interval=5
Cost0=100;
OSPF_Interface
IP_Address=10.138.99.*
Subnet_mask=255.255.255.240
MTU=8000
Router_priority=10
Cost=50
;

If you have multiple similar interfaces
with IP addresses within a reasonable
grouping, consider using a wildcard
interface definition, like this one that
replaces the OSA definition on the
previous slide. This way you can write
one statement to configure multiple
interfaces.
When matching its definitions to stack interfaces,
OMPROUTE first looks for an exact match, then for a
wildcard, picking the most specific one that matches.
Since the name is not required on
wildcard interfaces, they are also handy
for interface types with generated
names (like XCF Hipersockets)

Sample OMPROUTE configuration file: IPv6 OSPF
IPv6_OSPF
Router_ID=20.1.70.14
;
IPv6_Area
Area_number=61.61.61.61
Stub_area=yes
Import_Summaries=no
;
IPv6_Area
Area_number=0.0.0.0
;
IPv6_AS_Boundary_Routing
Import_Static_Routes=YES
Import_RIP_Routes=YES
;

Remember in IPv6 this is an arbitrary
value, not related to any interfaces. The
only requirement is that it be unique
throughout the IPv6 OSPF Autonomous
System.
IPv6 OSPF definitions are very similar
to their IPv4 equivalents!
Like IPv4, the IPv6 backbone area is
always 0.0.0.0

Sample OMPROUTE configuration file: IPv6 OSPF Interfaces
IPv6_OSPF_Interface
Name=OSA6*
Router_priority=0
Hello_interval=5
Cost0=100;
IPv6_OSPF_Interface
Name=VIPA6*
;

Because IPv6 addresses are dynamic
and often auto-configured, IPv6
interfaces are defined to OMPROUTE by
name only. OMPROUTE learns the
interface’s IP addresses and prefix
lengths from the stack. Names can be
explicit or wildcard, as shown here.
NO MTU definition either.. For IPv6
OMPROUTE learns that from the stack
as well.
Because OMPROUTE learns so much more information from
the stack about IPv6 interfaces, and because they are defined
by names, IPv6 interface definitions are usually much simpler
in OMPROUTE than their IPv4 equivalents

Sample OMPROUTE configuration file: Generic Interfaces
IPv6_Interface
Name=TRLAN6*
;
Interface
IP_Address=10.1.1.14
Name=PRIVATE4
Subnet_mask=255.255.255.0
MTU=1500;

The Interface statement (not to be confused
with the INTERFACE statement in the TCP/IP
profile) is used to define interfaces over which
no dynamic routing protocol will be run. For
example, a private network over which only
static routes will be used. When these
interfaces come up, OMPROUTE will add a
connection route to the interface’s subnet.
For IPv4 the main reason for this definition is to set the subnet mask and MTU. If
not defined OMPROUTE will use the class mask (which in the sample above would
be 255.0.0.0) and an MTU of 576, which could result in undesirable connection
routes being added to the routing table.
In the above example without the subnet mask and MTU defined to OMPROUTE,
when PRIVATE4 comes up OMPROUTE would add a route to 10.0.0.0 with an MTU
of 576 to the stack’s routing table which for destinations in the 10. network. This
route would take precedence over any default routes in the routing table for hosts
in that network, which is not likely what was intended.

Sample OMPROUTE configuration file: RIP definitions
RIP_Interface
IP_address=10.72.134.14
Name=OSAQDIO1A
Subnet_mask=255.255.255.128
MTU=1500
In_Metric=2;
IPv6_RIP_Interface
Name=HSOCKT*
Subnet_mask=255.255.255.240
In_Metric=1
;

In the interest of time we won’t go over RIP definitions
in detail here. Suffice to say they are analogous to
OSPF definitions in most ways, except they specify RIP
information for interfaces.
Remember, in RIP a distance
of 16 means infinity, so there
isn’t a lot of flexibility in
setting these values. Usually 1
(the default) is used.

Monitoring OMPROUTE
§ OMPROUTE has an extensive set of display commands to help you see what’s
going on with dynamic routing

§ OMPROUTE’s displays are accessed through the D TCP/IP command

§ D TCPIP,tcpipjobname,OMPROUTE,omproute_display_command…

§ Shortcut: OMPROUTE displays can also be done through the MODIFY
OMPROUTE command, i.e.,

§ F omproutejobname,omproute_display_command

§ OMPROUTE has displays to:

§ Display OMPROUTE’s internal routing table

§ Display interface information

§ Display neighbor information

§ Display topology database information

RTTABLE: display OMPROUTE’s internal routing table
D TCPIP,,OMPROUTE,RTTABLE
EZZ7847I ROUTING TABLE
TYPE DEST NET MASK COST AGE NEXT HOP(S)
SPF 2.2.2.0 FFFFFFFC 3 1380 9.67.106.4
SPF 2.2.2.2 FFFFFFFF 3 1380 9.67.106.4
RIP 6.6.6.4 FFFFFFFC 2 30 9.67.103.6
SPIA* 7.7.7.4 FFFFFFFC 3 1380 9.67.106.4
DIR* 9.67.100.0 FFFFFF00 1 1576 9.67.100.7
SPF 9.67.100.7 FFFFFFFF 2 1545 CTC7TO8
SPE2 10.1.1.0 FFFFFF00 0 1379 9.67.106.4
SPE2 10.1.1.1 FFFFFFFF 0 1379 9.67.106.4
SPE2 130.202.0.0 FFFF0000 0 1379 9.67.100.8 (2)
An interface name
instead of a next hop IP
address indicates a
direct route
This indicates that there
are actually two equal
cost routes to this
destination
This displays OMPROUTE’s internal routing table. This is not the
stack’s routing table. OMPROUTE uses this table as the basis for
building the stack’s table. Primary types are:
• SPF – route computed from local area topology using Djikstra algorithm
• SPIA – summary route to destination in another area, from an area-border router
• RIP – route computed using RIP
• SPEx – OSPF external route (imported by an AS Boundary Router)
• STAT – static route from the stack
• RSTA – Replaceable static route from the stack
Notes: for the IPv6 routing table, use RT6TABLE display command
This route table edited for space so it’s not complete

RTTABLE: display routes for a specific destination
D TCPIP,,OMPROUTE,RTTABLE,DEST=9.68.101.66
EZZ7874I ROUTE EXPANSION 370
DESTINATION: 9.68.101.0
MASK: 255.255.255.0
ROUTE TYPE: SPF
DISTANCE: 6
AGE: 1344
NEXT HOP(S): 9.167.100.17 (CTC2)
9.168.101.4 (CTC1)
Note the apparent mismatch.
OMPROUTE does not have a
host route for this destination
and this subnet route is the
most specific route available so
it is what is shown.
If there are multiple equal cost routes for a destination, this
display will show them all. OMPROUTE provides all equal
cost routes to the stack, and the stack makes any round-robin
decisions based on the configured IPCONFIG MULTIPATH
value.

Display summary OSPF interface information
D TCPIP,,OMPROUTE,OSPF,IFS
EZZ7849I INTERFACES 354
IFC ADDRESS PHYS ASSOC. AREA TYPE STATE #NBRS #ADJS
9.168.100.3 CTC1 0.0.0.0 P-P 16 0 0
9.167.100.13 CTC2 2.2.2.2 P-P 16 1 1
10.1.1.1 OSAGBE1 3.3.3.3 BRDCST 32 4 2
12.1.1.1 VIPA1A 3.3.3.3 VIPA N/A N/A N/A
Remember the designated router
architecture discussed earlier.
There are four other routers/hosts
on this LAN, but this host only
becomes fully adjacent to the DR
and the BDR, which is why these
numbers are different.
Interface state values are
documented in IP System
Admin Commands. State 32
indicates “not a designated
router”

Display detailed OSPF interface information
D TCPIP,,OMPROUTE,OSPF,IF,NAME=OSAQDIO1A
EZZ7850I INTERFACE DETAILS 356
INTERFACE ADDRESS: 9.168.100.3
ATTACHED AREA: 0.0.0.0
PHYSICAL INTERFACE: OSAQDIO1A
INTERFACE MASK: 255.255.255.0
INTERFACE TYPE: BRDCST
STATE: 32
DESIGNATED ROUTER: 9.168.100.1
BACKUP DR: 9.168.100.2
DR PRIORITY: 0 HELLO INTERVAL: 20 RXMT INTERVAL: 10
DEAD INTERVAL: 80 TX DELAY: 1 POLL INTERVAL: 0
DEMAND CIRCUIT: OFF HELLO SUPPRESS: OFF SUPPRESS REQ: OFF
MAX PKT SIZE: 556 TOS 0 COST: 100 DB_EX INTERVAL: 256
AUTH TYPE: CRYPTO-MD5
# NEIGHBORS: 4 # ADJACENCIES: 2 # FULL ADJS.: 2
# MCAST FLOODS: 0 # MCAST ACKS: 0 # MAX ADJ. RESETS: 0
# ERR PKTS RCVD: 0
NETWORK CAPABILITIES:
BROADCAST
MULTICAST
Tells you who the DR and
BDR are on this LAN
Configuration
information
Someone forgot to configure the
MTU value so OMPROUTE used
the default. This was probably not
the intended result and is causing
excessive fragmentation

Displaying other types of interfaces
§ There are similar displays for RIP interface information, as well as IPv6
equivalents. In the interest of time we won’t go over them here but they are
very similar

§ D TCPIP,,OMPROUTE,RIP,IFS
§ D TCPIP,,OMPROUTE,RIP,IF,NAME=
§ D TCPIP,,OMPROUTE,IPV6RIP,IFS
§ D TCPIP,,OMPROUTE,IPV6RIP,IF,NAME=
§ D TCPIP,,OMPROUTE,IPV6OSPF,IFS
§ D TCPIP,,OPMROUTE,IPV6OSPF,IF,NAME=
§ D TCPIP,,OMPROUTE,GENERIC,IF
§ D TCPIP,,OMPROUTE,GENERIC6,ALL

Note: GENERIC refers to interfaces defined to OMPROUTE using the
INTERFACE statement (i.e., not OSPF or RIP)

Displaying OSPF neighbor information
D TCPIP,,OMPROUTE,OSPF,NBRS
EZZ7851I NEIGHBOR SUMMARY
NEIGHBOR ADDR NEIGHBOR ID STATE LSRXL DBSUM LSREQ HSUP IFC
199.11.80.109 197.11.108.17 128 0 0 0 OFF OSAQDIO1
199.11.80.108 197.11.108.1 128 0 0 0 OFF OSAQDIO1
199.11.80.105 197.11.105.15 8 0 0 0 OFF OSAQDIO1
199.11.80.104 197.11.104.14 8 0 0 0 OFF OSAQDIO1
199.11.80.103 197.11.104.33 8 0 0 0 OFF OSAQDIO1
These are the neighbor states discussed earlier
Neighbor relationships are important to the functioning of OSPF
because it’s how a router learns network topology. So this display is
handy for making sure we’re communicating with other routers.
In this simplified example, the z/OS host has one OSA interface with
five neighbors. The top two in the list are the DR and BDR, so those
are the ones OMPROUTE becomes fully adjacent with. The other
neighbors remain in state 8, 2-way, meaning we are all seeing each
other’s HELLO (keepalive) packets

Detailed neighbor display
D TCPIP,,OMPROUTE,OSPF,NBR,IPADDR=9.67.100.17
EZZ7852I NEIGHBOR DETAILS 360
NEIGHBOR IP ADDRESS: 9.167.100.17
OSPF ROUTER ID: 9.67.100.7
NEIGHBOR STATE: 128
PHYSICAL INTERFACE: OSAQDIO1
DR CHOICE: 9.67.100.17
BACKUP CHOICE: 9.67.100.1
DR PRIORITY: 200
NBR OPTIONS: E,DC (0X22)
DB SUMM QLEN: 0 LS RXMT QLEN: 0 LS REQ QLEN: 0
LAST HELLO: 1 NO HELLO: OFF
# LS RXMITS: 1 # DIRECT ACKS: 2 # DUP LS RCVD: 2
# OLD LS RCVD: 0 # DUP ACKS RCVD:0 # NBR LOSSES: 0
# ADJ. RESETS: 2 # ERR LS RCVD: 0
This is who the neighbor
thinks owns these roles.
If they disagree with
local values, a problem
is likely
This is the local
interface over which this
host is adjacent to this
neighbor
This display allows you to
further explore OMPROUTE’s
relationship with a neighboring
router

More displays
§ There is a large set of displays for displaying the topology database information
as known by OMPROUTE. In the interest of time, these displays are beyond the
scope of this presentation but they are well documented, with samples, in the IP
System Administrator’s Guide.

§ D TCPIP,,OMPROUTE,OSPF,AREASUMM
§ D TCPIP,,OMPROUTE,OSPF,DATABASE,AREAID=…
§ Displays an area’s topology database

§ D TCPIP,,OMPROUTE,OSPF,EXTERNAL
§ D TCPIP,,OMPROUTE,OSPF,LSA…
§ Displays speciﬁc received topology advertisements

Note: All of the OSPF displays discussed in this presentation have IPv6
equivalents. Just substitute IPV6OSPF for OSPF in the statement
syntax.

IP Routing on z/OS

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