IS-IS (CLNS) not working over GRE tunnel in IOS-XR

[Alfonso Lopez]

We are having trouble setting up an IS-IS adjacency across a GRE tunnel, whose endpoints are a couple of IOS-XRv devices.

The GRE tunnel is going across an MPLS cloud.

The tunnel endpoints are reachable. Actually, OSPF is working fine across the GRE tunnel.

Here´s the extract of the configs and I´m ataching the full configs.

XR1
router isis 1
is-type level-2-only
net 49.0000.0000.0011.00
address-family ipv4 unicast
metric-style wide
interface Loopback1
passive
address-family ipv4 unicast
int tunnel-ip 1113
point-to-point
address-family ipv4 unicast
int tunnel-ip 1114
point-to-point
address-family ipv4 unicast

XR3

router isis 1
is-type level-2-only
net 49.0000.0000.0013.00
address-family ipv4 unicast
metric-style wide
interface Loopback1
passive
address-family ipv4 unicast
int tunnel-ip 1213
point-to-point
address-family ipv4 unicast
int tunnel-ip 1113
point-to-point
address-family ipv4 unicast

Thank you in advance.

Alfonso

[Evgeniy Prichinin]

It is related to clns mtu. 

try to set lsp-mtu under router isis process configuration.

[Joseph W. Doherty]

I agree with Evgeniy, it's likely an MTU issue. (I haven't done an IS-IS on a GRE tunnel on a XR, but I have on IOS platforms. Those generally need the MTU configured on the interface.)

[Alfonso Lopez]

Hi Evgeniy, thanks for the quick reply.

I just tried setting MTU to 1400 and then to 1300, but no luck. Still no adjacency.

RP/0/0/CPU0:XR1#sh isis neighbors
Thu Feb 28 09:43:00.003 UTC

IS-IS 1 neighbors:
System Id Interface SNPA State Holdtime Type IETF-NSF

Everything else looks fine, right?

The GRE tunnel is reachable even with an mtu of 1450 without fragmentation:

RP/0/0/CPU0:XR1#ping 192.168.113.13 size 1450 df-bit
Thu Feb 28 09:35:24.595 UTC
Type escape sequence to abort.
Sending 5, 1450-byte ICMP Echos to 192.168.113.13, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/9/29 ms

Here's the current config of one side (replicated on the other side):

router isis 1
is-type level-2-only
net 49.0000.0000.0011.00
log adjacency changes
lsp-mtu 1300
address-family ipv4 unicast
metric-style wide
mpls ldp auto-config
!
interface Loopback1
passive
address-family ipv4 unicast
!
interface tunnel-ip1113
point-to-point
address-family ipv4 unicast

interface tunnel-ip1114
point-to-point
address-family ipv4 unicast

Thank you.

Alfonso

[Harold Ritter]

Hi Alfonso,

I have this working perfectly well with XRv 6.1.3. You might want to run some debugs to see what is going on.

Regards,

[Alfonso Lopez]

Well, I'm doing this with XRv 6.1.2. 

Is your IS-IS adjacency going over a GRE tunnel as well?

If so, could you please share your full config?

"debug isis adjacencies" is not showing anything:

RP/0/0/CPU0:XR1#show debug
Sat Mar 2 17:40:47.982 UTC

#### debug flags set from tty 'vty0' ####
clns events flag is ON with value 0
isis adjacencies flag is ON with value 'unfiltered'

Is that an indication of something?

Regards.

Alfonso

[Alfonso Lopez]

Apparently it's not MTU related.

Any more ideas?

Anyone?

[Georg Pauwen]

Hello,

on a side note, when I configure the router, the system displays the message below and adjusts the MTU automatically.

Can you post the output of:

show isis interface tunnel-ip1113

from both sides ?

RP/0/0/CPU0:XR2#RP/0/0/CPU0:Mar 15 11:42:04.101 : isis[1010]: %ROUTING-ISIS-4-SNPTOOBIG : L2 SNP size 1492 too big for interface tunnel-ip1113 MTU 1476, trimmed to interface MTU