Symptom
+ Duplicates in pathtrace will be seen:
B# pathtrace nve mac aa:aa:aa:aa:aa:bb 200 verbose max-ttl 100
Path trace Request to peer ip 10.21.0.10 source ip 10.11.0.10
Sender handle: 5
Hop Code ReplyIP IngressI/f EgressI/f State
======================================================
1 !Reply from 10.1.1.6, (SPINE) Eth1/51 Eth1/53 UP / UP
2 !Reply from 10.1.1.6, (SPINE) Eth1/51 Eth1/53 UP / UP
3 !Reply from 10.21.0.10, (D) Eth1/35 Vlan200 UP / UP
+ There can be multiple hops duplicated
Conditions
+ VXLAN VPC VTEP
+ Pathtrace is initiated from one of VPC peers.
+ TTL exceeded message which is sent back from any of the hops on the path is received on VPC node which is not the source of pathtrace. (Pathtrace initiated from VPC-1 and TTL exceeded message is reaching VPC-2 due to Spine having two paths towards IP which was used as source IP in pathtrace)
Workaround
There is no efficient workaround available currently.
Further Problem Description
+ It looks like the problem is related to VIP address being used as source IP by NGOAM
+ This simply means that for TTL-exceeded messages we will have two paths to reach VIP address as it is same for both VPC peers.
+ If we would use PIP address as the source IP in pathtrace then this address would be unique and all of the TTL exceed messages would be send back to VPC node which is initiating pathtrace.
+ Currently we cannot even force PIP address to be used as source IP in pathtrace:
B# pathtrace nve mac aa:aa:aa:aa:aa:bb 200 verbose max-ttl 100 source 10.11.0.11
Path trace Request to peer ip 10.21.0.10 source ip 10.11.0.10
Sender handle: 7
Hop Code ReplyIP IngressI/f EgressI/f State
======================================================
1 !Reply from 10.1.1.6, (SPINE) Eth1/51 Eth1/53 UP / UP
2 !Reply from 10.1.1.6, (SPINE) Eth1/51 Eth1/53 UP / UP
3 !Reply from 10.21.0.10, (D) Eth1/35 Vlan200 UP / UP
10.11.0.11 - PIP address
10.11.0.10 - VIP address
+ If hashing is correct (all of the TTL exceeded messages are coming back to the VPC node which initiated pathtrace, then there will be no duplication seen)
