Hi Cisco eXPerts.
I'm having an issue with a GRE tunnel on the Cisco NCS-5502-SE router running the IOS-XR 7.3.2 64 bits.
This is my scenario
[server-a] ==> [core-router-1] === GRE tunnel ===== [ internet ] ===== GRE === [edge router] <== [server-b]
linux <=== [ASR9004-7.3.2] ====================================== [NCS5502-SE-7.3.2] ===> linux
So basically, I'm trying to send large packets [1500bytes] from server-a to server b, transversing the GRE tunnel via the internet.
Any packet in the 1476 bytes size goes through the GRE tunnel with no issues. But if I try anything larger than 1476, it doesn't work.
It sees that the issue is with the NCS5500, as if I send packets from server-a to server b I'm able to see the packets arriving at server-b using tcpdump. But the other way around won't work.
I'm also unable to ping the /31 address of the remote interface using packets larger than 1476. So the issue for me is the NCS5502-SE not able to fragment packets larger than 1476 when forwarding it through the tunnel.
The configuration is pretty basic, but I'll share below:
Router A(Core Router - ASR9k
interface tunnel-ip5
mtu 1500
vrf MY-VRF
ipv4 address X.X.X.14 255.255.255.254
ipv4 tcp-mss-adjust enable
tunnel mode gre ipv4
tunnel source Bundle-Ether498
tunnel destination X.X.X.212
Router B (NCS5500):
interface tunnel-ip5
mtu 1500
ipv4 address X.X.X.15 255.255.255.254
load-interval 30
tunnel mode gre ipv4
tunnel source TenGigE0/0/0/22/0
tunnel destination X.X.X.238
