Re: ICMP Router Discovery
Re: ICMP Router Discovery
- Subject: Re: ICMP Router Discovery
- From: Allen Smith <email@hidden>
- Date: Wed, 29 Jun 2005 08:19:41 -0700
There might not be a router. There are stub networks out there that have no
routers. There could be multiple routers on each of the networks those
interfaces are connected to. If they aren't configured on the host, it won't
know about them and depending on the configurations of the routers, they may
not advertise their presence.
There are ways to try and find a router that is not configured on the host.
None are sure-fire, few are easy, and some will only a small chance of
finding something. A few could cause badness in local network if the routers
are too trusting.
1) Join one of the mcast groups related to routers and listen for traffic:
224.0.0.2 All routers on this subnet
224.0.0.5 OSPF routers
224.0.0.6 OSPF designated routers
2) Listen for OSFP/ISIS/RIP/EIGRP hello type packets. Senders are likely
routers.
3) icmp router discover (RFC1256).
4) scan local network for hosts and use SNMP (hope for public read-only) to
see if the device is a router.
5) send DHCP requests on all ports, see if you get back any router entries for
that interface.
6) Fire up RIP/OSPF/ISIS and see if you can talk to anyone.
7) scan local network and then try sending icmp requests to a remote ip
through each of the hosts, if you get a positive response then you've found a
router, if you get an icmp-redirect then you've found two!
Without further context it's really not possible to come up with a better
answer, and even with context it might just be a problem without a complete
solution.
-Allen
On Tuesday 28 June 2005 06:00 pm, Chase wrote:
> On Jun 28, 2005, at 7:13 PM, Justin C. Walker wrote:
>
> > Can you describe your goals?
>
>
> the goal is simply to get a router address for a given interface.
>
> i have a list of interfaces. some have ip addresses. some don't.
> for those that do, i need the gateway address that they are connected
> to.
>
> that's all.
>
> - chase
>
>
>
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