Feature request: CARP awareness in BIRD?

[Thomas Steen Rasmussen]

On 6/3/22 5:40 PM, Ondrej Zajicek wrote:
> 
> That is an interesting idea, and from your description it seems like not
> hard to support, esp. if that is just some kind of flag on iface/address.

That is what I was hoping for :)

> 
> But i do not have experience with this, so i have some questions:
> 
> 1) it is per-iface state or per-address state?

It is a per-address state (actually it is per VHID state, where each 
VHID is a group of 1-N IP addresses, and each interface can have 1-N VHID).

> 
> 2) Could you send me output of ifconfig for master/backup/non-carp iface
> for comparison?
> 

Absolutely. This is interface lagg0.2002 which has a single VHID, first 
node A which is MASTER:

-----------------------------
[tykling at dgncr2a ~]$ ifconfig lagg0.2002
lagg0.2002: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> 
metric 0 mtu 1500
         description: tyktech infrastructure servers vlan 2002 - 
85.209.118.0/28 and 2a09:94c4:55d1:7600::/64
         options=4600003<RXCSUM,TXCSUM,RXCSUM_IPV6,TXCSUM_IPV6,NOMAP>
         ether 3c:ec:ef:46:e1:58
         inet6 fe80::3eec:efff:fe46:e158%lagg0.2002/64 scopeid 0x11
         inet6 2a09:94c4:55d1:7600::2a/64
         inet6 2a09:94c4:55d1:7600::1/64 vhid 5
         inet 85.209.118.1/28 broadcast 85.209.118.15 vhid 5
         groups: vlan carp
         carp: MASTER vhid 5 advbase 1 advskew 100
         vlan: 2002 vlanproto: 802.1q vlanpcp: 0 parent interface: lagg0
         media: Ethernet autoselect
         status: active
         nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
[tykling at dgncr2a ~]$
-----------------------------

and then node B which is BACKUP:

-----------------------------
[tykling at dgncr2b ~]$ ifconfig lagg0.2002
lagg0.2002: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> 
metric 0 mtu 1500
         description: tyktech infrastructure servers vlan 2002 - 
85.209.118.0/28 and 2a09:94c4:55d1:7600::/64
         options=4600003<RXCSUM,TXCSUM,RXCSUM_IPV6,TXCSUM_IPV6,NOMAP>
         ether 3c:ec:ef:46:e0:b8
         inet6 fe80::3eec:efff:fe46:e0b8%lagg0.2002/64 scopeid 0xf
         inet6 2a09:94c4:55d1:7600::2b/64
         inet6 2a09:94c4:55d1:7600::1/64 vhid 5
         inet 85.209.118.1/28 broadcast 85.209.118.15 vhid 5
         groups: vlan carp
         carp: BACKUP vhid 5 advbase 1 advskew 100
         vlan: 2002 vlanproto: 802.1q vlanpcp: 0 parent interface: lagg0
         media: Ethernet autoselect
         status: active
         nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
[tykling at dgncr2b ~]$
-----------------------------

As you can see CARP is not really an interface, it is more like a 
property of an IP. Each node has both CARP IPs (marked with a vhid N at 
the end of the line) and non-CARP IPs (in this example the only non-CARP 
IP is for ipv6).

An interface can have multiple VHIDs which can be MASTER or BACKUP 
independent of eachother.

 From birdc the "show interfaces" for these look like this:

On the MASTER (A) node:
-----------------------------
lagg0.2002 up (index=17)
         MultiAccess Broadcast Multicast AdminUp LinkUp MTU=1500
         85.209.118.1/28 (Preferred, scope univ)
         fe80::3eec:efff:fe46:e158/64 (Preferred, scope link)
         2a09:94c4:55d1:7600::2a/64 (Preferred, scope univ)
         2a09:94c4:55d1:7600::1/64 (scope univ)
-----------------------------

On the BACKUP (B) node:
-----------------------------
lagg0.2002 up (index=15)
         MultiAccess Broadcast Multicast AdminUp LinkUp MTU=1500
         85.209.118.1/28 (Preferred, scope univ)
         2a09:94c4:55d1:7600::2b/64 (Preferred, scope univ)
         fe80::3eec:efff:fe46:e0b8/64 (Preferred, scope link)
         2a09:94c4:55d1:7600::1/64 (scope univ)
-----------------------------

As you can see they are considered equally valid which causes BIRD to 
think it has a usable IP for the prefix even though it does not.

> 
> 4) What is a general behavior of backup ifaces/ips? Are they usable, or
> it is more like iface that is AdminUp/OperDown (in SNMP terminology)?

The interfaces as such are fully usable, but the OS will not respond to 
ARP/NDP for virtual IPs in a BACKUP VHID. The OS still permits binding 
to them (so daemons can bind and be running and ready on BACKUP nodes).

Best regards,

Thomas Steen Rasmussen