Dear all,
hopefully this might be an easy question for whoever deals with Nexus switches. I have noticed the following about the isis protocol and how nexus 7K seems to set the router-id for this protocol and i would like clarifications from you if possible.
Within the LSPs that ISIS creates, the router ID seems to be an ip address which is configured under a VRF interface and not the looback of the box. Of course I know that ISIS protocol and router ID concept are alike (router ID is set mainly for IP protocols, while ISIS utilizes as "router-id" the NET address. Hence, you cannot set actually the router ID in ISIS like you do explicitly with CLI for OSPF and EIGRP.
You may see below the commands taken out of a nexus 7K, that I'm operating.
nexus7K1# show isis database detail
…output omitted….
nexus7K1.00-00 * 0x00042CCD 0x0515 720 0/0/0/3
Instance : 0x00004A4D
Area Address : 49.0001
NLPID : 0xCC
Router ID : 192.168.1.251
IP Address : 192.168.1.251
Hostname : nexus7K1 Length : 9
…output omitted….
nexus7K1# show running-config interface vlan 107
!Command: show running-config interface Vlan107
!Time: Mon Mar 23 16:28:54 2015
version 5.2(5)
interface Vlan107
no shutdown
description xxxxx
vrf member MGMT
no ip redirects
ip address 192.168.1.251/24
hsrp version 2
hsrp 107
priority 255
ip 192.168.1.240
As a result in other network routers, we may see that networks towards Nexus are advertised with the router id 192.1681.251
E.g for IP address 194.30.193.3 @ Nexus7k1 (vlan xx)
RP/0/RSP0/CPU0:CRS-00#show route 194.30.193.3
Routing entry for 194.30.193.0/24
Known via "isis 3329", distance 115, metric 40, type level-2
Installed Mar 5 06:00:26.487 for 2w4d
Routing Descriptor Blocks
62.38.93.97, from 192.168.1.251, via TenGigE0/1/0/0
Route metric is 40
No advertising proto
Do you know why this is happening? Or what is the reason for nexus picking over this IP address (under a VRF?) for ISIS protocol router-id? Is it some kind of default mechanism picking over specific e.g max or lower IP address from those configured?
I couldn't locate any useful information in Nexus 7K configuration guide regarding ISIS router-id concept.
http://www.cisco.com/c/en/us/td/docs/switches/datacenter/sw/5_x/nx-os/unicast/configuration/guide/l3_cli_nxos/l3_isis.html#wp1063980
I have searched the running configuration to find out the whole banch of IP addresses configured. The above address lies in the middle so nor max or lowest rule is followed:
ip address 10.112.60.2/24
ip address 194.30.193.3/24
Finally, do you know any way to configure explicitly this via CLI in order to be the loopback?
Thanks in advance
Dimitris
