Cisco ISR 4k BFD Session Host: Software

While deploying BFD on some ISR 4k’s I noticed this “Session Host: Software”. It turns out that BFD Echo mode is not hardware offloaded on these ISR 4K’s, only the Control packets are. Although the echo packet is routed via CEF on the neighbor, when it comes back to us we process it in software. This is in contrast to the Control function which is a ping back and forth on udp port 3784, this is ASIC processed.

This is a big contrast to a lot of the learning material regarding the echo function and why it’s so good. So if you’re platform supports echo function in hardware, do that. Otherwise, disable it and use the control packets for the event triggering as long as they are hardware offloaded.

Per the Cisco Document:

https://www.cisco.com/c/en/us/td/docs/routers/access/4400/software/configuration/xe-16-7/isr4400swcfg-xe-16-7-book/configuring_high_availability.html

Configuring BFD Offload

Restrictions
  • Only BFD version 1 is supported.

  • Only Asynchronous mode or no echo mode of BFD is supported.

  • BFD hardware offload is supported for IPv4 sessions with non-echo mode only.

 

The original config:

bfd template single-hop BFD
interval min-tx 300 min-rx 300 multiplier 3
echo
int g0/0/1
bfd-template BFD

 

Which caused this:Screenshot 20180722 175223

 

To resolve this it required the following config:

bfd template single-hop BFD
interval min-tx 300 min-rx 300 multiplier 3
no echo
int g0/0/1
bfd-template BFD

note: we basically just turned off the echo function

And then I had to flap the interfaces on both sides

 

Screenshot 20180724 104223

 

 

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