Carp vhid with vlan id's alignment

[Alexander V. Chernikov]

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Rafael Ganascim wrote:
> Hi list,
> 
> I'm planning and testing a new FreeBSD router, with vlans and carp
> interfaces. There are a lot of vlans, with high vlan IDs. We have, for
> example:
> 
> dot1q vlan id: 1530
> 
> Iface igb0
>  vlan1530
>   carp1530
>    vhid 10
> 
> What do you think in change the carp code to support vhid above 255 (just to
> align with vlanid, carp vlan name)? I think that it can ease the
> troubleshooting, standardization and documentation (in this scenario). It's
> the last piece of the complete 'id' alignment.
1) CARP packet format uses 8bit for VHID (see sys/netinet/ip_carp.h for
packet format)

2) Making carp instance for every vlan is (generally) wrong design.
Making single carp instance for group of interfaces (and
creating/deleting vlans depending carp instance state) is more
preferable in most cases. You can get state change events for carp(4)
interfaces via devd(8).

Moreover, every carp instance sends multicast packets every 1 second +
several milliseconds in default scenario. This means a lot of multicast
traffic in case of many instances which can confuse other devices (or
another carp implementations like ucarp).

> 
> But I don't know the impact of this change in the source codes (and related,
> like the ifconfig).
> 
> What do you think?
> 
> 
> Regards,
> 
> Rafael
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