[crossbow-discuss] Re: [clearview-discuss] IPMP and Crossbow

[Thirumalai Srinivasan]

Iam wondering about the  IPMP <--> VNIC feature interaction.

If vnic1 and vnic2 are in the same IPMP group, IP requires that vnic1 
and vnic2
be completely equivalent from an IP perspective, i.e. anything reachable via
vnic1 is also reachable via vnic2 and vice-versa. Also vnic1 and vnic2 
must be
on the same broadcast domain.

If vnic1 and vnic2 are plumbed over the same underlying physical NIC, the
above conditions are satisified. But this case does not seem to be highly
useful, since an underlying NIC failure will impact both vnics and there 
isn't
any real multipathing here.

If vnic1 and vnic2 are plumbed over different physical NICs, then we have
2 sub-cases.

i. vnic1 and vnic2 are the only vnics over the respective physical NICs.
   This satisfies the IPMP requirements. This subcase also means an
   underlying NIC failure can be translated to a vnic failure. Generating
   a DL_NOTE_LINK_DOWN is not an issue in this case.

ii.There are some other vnics on either or both of the physical NICS apart
   from vnic1 and vnic2. This subcase violates the IPMP requirements, since
   some destinations are locally reachable from vnic1 and not from vnic2 and
   vice-versa. vnic1 and vnic2 are not really equivalent from IP's 
perspective,
   unless we have those (v)bridge across the vnics over different 
physical NICs.
   But that makes assumptions about the vnic configurations and what is
   permitted.
  
Thirumalai
 
Steffen Weiberle wrote:

> Regarding the VNIC part of crossbow, I imagine IPMP should work, and 
> will have to try that.
>