[nsp] HSRP and VLANs

[Marco Matarazzo]

> There's nothing that says the VIP has to be in the same subnet as the
> physical interface addresses, so yes, you can use RFC1918 addresses as the
> two physical interface addresses, and the VIP is then simply taken from
the
> customer's public assigned subnet.  This way you don't use any extra IP
> addresses from the customers public space.

Uhm... it seems interesting Robert, but I don't know how I could integrate
it in my current config... what I'm doing now is create subinterfaces for
each customer, with it's own IP space (say 80.80.80.80/28) and vlan. If I
assign RFC1918 address to the subinterface, how will packet coming from the
outside routed to 80.80.80.80/28 if the directly connected interface has no
ip address in that range? I cannot even assign a subnet mask to a VIP
address... I think I missed something here! :O

Thanks!
]\/[arco

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of jlewis at lewis.org
Sent: 16 December 2003 14:18
To: Marco Matarazzo
Cc: cisco-nsp at puck.nether.net
Subject: Re: [nsp] HSRP and VLANs


On Tue, 16 Dec 2003, Marco Matarazzo wrote:

> > As I understand it, you need at least 3 IPs to do HSRP for one
> > subnet or VLAN.  One IP for each physical interface on the router
> > and one virtual IP which becomes the host's default gateway.  By the
> > sounds of it, you may need to expand the subnets for each of those
> > 50 VLANs (if you have promised each customer in the vlan 6 or 14
> > usable IP addresses, depending) for each  .  I don't know if you can
> > do unnumbered HSRP.

I haven't tried this, but what if you put the real IPs in a different
subnet (maybe even RFC1918 IPs) and the standby IP in the customer's
subnet?

> Good point Jason! But I wonder how one can deliver a point to point
> connection (I also have a couple of BGP downstreams) with a  /30, and
> have redundancy... there should been something we missed! At least I
> hope so! :)

If you mean a PTP T1 or other similar connection, PTP implies there are
only 2 devices connected.  If you mean a vlan where you used a /30 to give
yourself (gateway) 1 IP, and the customer 1 IP, then maybe the above idea
would work.

Is there a limit (other than the number of VLANs a router can support) on
the number of standby IPs that can be configured?

----------------------------------------------------------------------
 Jon Lewis *jlewis at lewis.org*|  I route
 Senior Network Engineer     |  therefore you are
 Atlantic Net                |
_________ http://www.lewis.org/~jlewis/pgp for PGP public key_________

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