Hi,
Why are PWHE interfaces not supported under router vrrp?
I have 2x ASR9K overlay VRRP gateways on my network, where I aggregate redundant colo customers from multiple data centers in the metro over MPLS fabric. Redundant ASR920s are situated at each data center, and I haul customer colocation connections via MPLS back to head-end ASR9K, in a setup as follows:
VRRP GW A (ASR9K) ---- { mpls cloud } --- ASR920 #A --+
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customer switch -- end-user host
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VRRP GW B (ASR9K) ---- { mpls cloud } --- ASR920 #B --+
The reason for this design is because I don't want to run VRRP and layer-3 internet gateway on cheap and TCAM-limited ASR920s out in the field, so I'd rather have that run on dedicated ASR9K VRRP GWs at the head-end POPs -- this is accomplished by backhauling customer colo connection via MPLS to ASR9K providing VRRP gateway. If the customer unplugs his connection, or a link-state to customer switch is lost, PWHE interface will be signaled down, causing VRRP to fail-over due to interface-down event at the ASR9K.
But the problem here is that IOS XR does not permit PWHE interfaces to be used under 'router vrrp'. As you can see in the above diagram, because the customer at the data center colo is providing layer-2 switch, the VRRP GW does not need to be concerned with switching -- so why shouldn't PWHE interface be able to participate in VRRP as a router host interface?
The workaround solution I am using is to use BVI interface instead at the ASR9K/VRRP GWs. This requires creation of VPLS bridge-domain instead of xconnect construct on ASR9K side (ASR920s can still build as PW construct, as VPLS at head-end is just L2 VFI mounted on top of local BD), but otherwise works very well with proper signaling of link-state for VRRP failover to work seamlessly.
The problem with having to use BVI for VRRP is the inability to use QoS shaping on BVI interfaces on XR. ASR920s have very terrible buffers (16MB shared for all ports), so it is better to provide traffic shaping further upstream on ASR9K, which I can do with PWHE. BVI does not have this capability, as there is no feature support to attach generic-interface-list onto a BVI interface.
Whhhy though?!?
