Incoming SSDP UDP 1900 filtering

Mon Mar 25 16:43:35 UTC 2019

Hey Tom,

> If your edge ingress ACLs are not 100% in sync all the time, you will inevitably have Really Weird Stuff happen that will end up taking forever to diagnose.

You may at some cases have hard to troubleshoot issues, which is true
for everything, even when perfectly configured, because software is
not perfect. However choosing to do iACL is still something many
networks choose to do, because the upside is worth the complexity to
them.

> Packet filtering is more computationally taxing than just routing is. Your edge equipment is likely going to be built for maximum routing efficiency. Trying to bite off too much filtering there increases your risk of legit traffic being tossed on the floor.

Depends on implementation, on some implementations it is zero-cost on
some it is not. On most implementations it's very cheap, particularly
compared to say uRPF. It seems your position is 'i don't know how ACL
works on my platforms and i don't trust myself to write ACL, so i
should not do them', which is perfectly valid position under those
constrains, but other networks have other constrains under which it is
no longer valid proposal to omit doing iACL.

I would encourage networks to continue deploying iACL and consider it
BCP. iACL removes attack surface and protects you from host of known
and unknown SIRT issues.

-- 
  ++ytti