Multiple bfd sessions for a path between 2 routers

[rakuten02]

From what I have read, if there are multiple bfd sessions between 2 routers, it means that there are multiple links between the 2 routers. I don't really understand this point.

Does this also mean that the traceroute result should have some differences if performed several times?

I tried traceroute several times, but each time the results are exactly the same. 

To further elaborate, the source and destination IP are the same. Destination port and uptime is different.

The device is Cisco Viptela Vedge.

[Kanan Huseynli]

Hi,

bfd runs over IPSec tunnel. So, first IPSec (or GRE) tunnels are built between interfaces (TLOC) ,then BFD runs over it (in encrypted form).

While you do traceroute, TLOC information are not shown. So, in your both cases, since remote router is the same ,it each time shows the same result (remote router responds with service interface IP, not with tunnel IP).

There is "show policy service-path vpn [] interface [] source-ip [] destination-ip [] protocol [] dscp [] all" command that shows all available paths for the traffic flow. You can remove "all" keyword and see which tunnel will be used.

By default, router does ECMP hashing (chooses path) using source&destionation IP, protocol, DSCP value. Hence, in above command you should enter all value to see actual result (but this is simulation, no real data traffic sent).

HTH,

[rakuten02]

Thanks a lot for the reply. 

I noticed that the other bfd session for the path between these 2 routers have the same TLOC (system ID, color and encapsulation type). 

Shouldn't each bfd session have a different TLOC? 

Under show tunnel statistics, there are also 2 tunnels for that color with all parameters the same. Only the tx and rx packets are different.

[Kanan Huseynli]

Hi,

could you share:

show bfd sessions

show tunnel statistics

sh run vpn 0

Regards,