Some observations/questions on inter-subnet and type-5 draft for EVPN

[Antoni Przygienda <[e-mail]>]

So, wrapping around my head around EVPN type 5 and inter-subnet drafts and some observations (all on version -02 of type  5 and version -04 of inter-subnet)


a)       Nitpick first: in type-5 section 3.1 the IP Address Length field is not a particularly well chosen name for the field. It really is prefix length and other drafts use IP Address Length being 1 byte to indicate 4 bytes or 16 bytes and not mask length (e.g. evpn-07). I suggest changing to 'IP Prefix Length' or something like this.


b)      The new BGP attribute have couple unclear things to it (I mean the 'EVPN-GW-2-EVPN-GW tunnel attribute' for lack of a clearly specified name (which I think it needs) in draft inter-subnet section 6)

i.       I assume the intention of lack of such an attribute is that the tunnel is MPLS and therefore the label-2=l3vpn-label since I don't see an 'MPLS-tunnel-type' in the attribute ? But then, how do we figure out e.g. the MAC of the NVE. Did I misread completely or is that an oversight or did I get lost in all the tunneling ?

ii.      Bump-in-the-wire-use-case seems to indicate that the 'EVPN-GW-2-EVPN-GW tunnel attribute' is carried on route type 1 (but it seems it could be carried on the type-5 route with ESI!=0 equally well ?  In the VRF-2-VRF case however it's clear that type-5 is carrying the tunnel attribute so it may be more consistent to not stick it on type-1 albeit sticking it on type-1 is more consistent with it being stuck on RT-2 routes to resolve the MAC-2-tunnel in e.g. floating ip use case

iii.     It is not clear whether multiple tunnel attributes can be sent within a route & used for load balancing



c)      I start to ask myself whether we should start to think about IP route preferences in EVPN. Observe that currently we can install/use IP addresses/prefixes for IRB in EVPN assigned VRFs from multiple sources (or rather inter-subnet route on them)


1.      IP-MAC (RT-2) containing /32 (incl. gateway attribute)

2.      RT-5 containting /0 all the way to /32

3.      Draft-inter seems to allow to use IP-VPN routes to be used for lookup incl. prefixes (if not explicitly then surely implicitly via RTs)

4.      Redistribution from other protocols that do either IP prefix or IP-MAC bindings (but that's kind of well-known protocol distance we have today already)


Question here becomes: Should we specify the IP route preferences for all those routes being installed into the IP-VRF (or in broader sense, which address type should be preferred in inter-subnet lookup) ?  If not, looping criteria start to become imaginable IMO if implementations do not agree on the protocol preference as was the case for a while in L3 routing.

thanks

--- tony