Dynamic cost?

Ondrej Zajicek santiago at crfreenet.org
Thu Dec 22 16:21:11 CET 2016

On Wed, Dec 21, 2016 at 01:09:44PM -0600, Michael McConnell wrote:
> Hello Mike,
> There is no concept of latency by peer in any main stream routing
> protocol because latency can be influenced by traffic load, which would
> create a real mess trying to understand the traffic flow. If you know one
> link is always lower latency than the next you simply set the cost
> manually at startup. 


That is true for real traffic latency, but there is another metric - base
latency (latency of link without any load). That is metric that makes
perfect sense, is stable (at least for 'real' links) and could be
reasonably estimated. You could use minimum of measured values as
any measured latency would be higher than ideal value.

OSPF and most other routing protocols do not have tools for latency
estimation. I guess BFD echo packets or even ping could be used for that.

But BIRD does not have any such features integrated.

> Cisco’s EIGRP protocol does have a load concept, but I believe Cisco pretty much says don’t use it (;

> If you really wanted to you could create a script that ran a manual
> test of the latency of each link, the script could then updated the cost
> value in bird and reconfigure it though.

There is one problem - Unless interfaces are PtP links, you would
probably need different latencies to different neighbors. That could be
generally done in OSPF with PtMP network type, but BIRD does not allow
to specify that.

Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
"To err is human -- to blame it on a computer is even more so."
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