ISIS between ( IOS-XE and IOS-XR) peer not establish

[Tareq Emad Al Asfoor]

Hi all , 

I have two router ( IOS-XE ( cisco 3850)  and IOS-XR ( ASR9K ) , These two router connected and i have VLAN1000 peering between them using OSPF ..  Now i need to use the same VLAN to enable ISIS with tag mpls between them.. I configured the two side as you can see below but i cant have neighbor between them , 

IOS-XE

router isis mpls
net 11.1111.1111.1111.1921.6820.5005.00
is-type level-2-only
metric-style wide level-2

!

interface Vlan1000
description To -ASR9K
ip address 10.10.10.1 255.255.255.252
ip router isis mpls
ip route-cache policy
end

IOS-XR

router isis mpls
is-type level-2-only
net 11.1111.1111.1111.1921.6820.5003.00
log adjacency changes
address-family ipv4 unicast
metric-style wide level 2

!

interface TenGigE0/0/1/0.1000
circuit-type level-2-only
!

interface TenGigE0/0/1/0.1000
ipv4 mtu 1500
ipv4 address 10.10.10.2 255.255.255.252
encapsulation dot1q 1000

SW-3850#sh ip ospf neighbor vlan 1000

Neighbor          ID        Pri State         Dead Time      Address          Interface
10.10.10.2        1        FULL/DR         00:00:39      10.10.10.2      Vlan1000

SW-3850#sh isis neighbors

Tag mpls:
System      Id       Type     Interface        IP Address       State   Holdtime     Circuit Id

So nothing appear in isis neighbors , plz any advice ,,

Kind Regards, 

Tariq.E

[Harold Ritter · Accepted solution]

The issue is that the CLNS MTU on the XR side is set to 9173, which is higher than the interface MTU (9100 for the physical interface and 1500 for the VLAN interface) on the XE side. You definitely need to lower that value on the XR side.

Regards,

[Tareq Emad Al Asfoor]

Well , i will check this issue and give you feedback .. Thanks ..

[Tareq Emad Al Asfoor]

Thanks for your replay. You are right , as soon as removed the MTU from XR interface the peer become up, now we are know the issue is MTU .. So, the problem now , i cant remove this MTU from XR side .. So is any way to increase the CLNS MTU from XE side on interface VLAN 1000 .. 

Thanks for your support .. 

[Harold Ritter]

Hi Tareq,

I'm glad it fixed the issue. You can definitely change the CLNS MTU on the XE side, but the CLNS MTU on the VLAN interface cannot obviously be larger than the physical interface MTU between the XE and XR devices. You will need to find what is the largest value that you can configure on the physical and the VLAN interface on the XE side and adjust the XR MTU accordingly.

Regards,

[Tareq Emad Al Asfoor]

Thanks for your support .. 

[kamyk]

Please rememer that IOS XR you always nedd to add L2 header under mtu command.

Example:

   routed interface MTU from IOS XE +14B.

on trunk interface MTU from IOS XE +14B (MAC)+4B (vlanTAG).