Re: ICMP Router Discovery
Re: ICMP Router Discovery
- Subject: Re: ICMP Router Discovery
- From: Andrew Gallatin <email@hidden>
- Date: Wed, 29 Jun 2005 08:31:28 -0400 (EDT)
Chase writes:
> 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.
As others have pointed out, an interface may not have any router
associated with it. Alternatively, an interface may have more than
one router associated with it.
Take en0 from my configuration for an example of an
interface with multiple routers:
It is configured with: inet 172.31.130.133 netmask 0xffff0000 broadcast 172.31.255.255
Interesting routes are:
default 172.31.128.254
172.31.192/19 172.31.128.254
This means that it *should* be able to talk to all hosts from
172.31.0.1 -> 172.31.254.254 directly. For IP addresses outside
that range, it will use the default router.
However, we started adding remote office VPNs in the range
172.31.{192,193,194, etc}. So we need to add an explicit route through
the VPN gateway to be able to talk to hosts on those subnets. This
is what the 172.31.192/19 route is for. It happens that the VPN
gateway is the same as our router, but this is a coincidence, not a requirement.
Take en1 from my configuration for an example of an
interface with no routers:
It is configured with inet: 10.0.130.133 netmask 0xffff0000 broadcast 10.0.255.255
There are no interesting routes. Eg:
netstat -rn | grep en1
10/16 link#6 UCS 3 0 en1
10.0.130.108 0:60:dd:49:93:ee UHLW 0 1 en1 1000
10.0.130.109 0:60:dd:49:95:ef UHLW 0 2 en1 1003
10.0.130.134 0:60:dd:48:f9:f0 UHLW 2 867834 en1 941
It intentionally has no routes added, because this is a private test
LAN for my company's network adaptors and there are no routes out of
it.
Drew
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