From: Doug Calton (dcalton@fuse.net)
Date: Tue Dec 10 2002 - 17:57:49 GMT-3
Sorry - this is just too complicated to explain. Let me back this up to a
more "theoretical" level. Let's say I have a PC attached to an Ethernet
interface of a router - say 192.168.1.0 network, and that the router is
attached via a serial interface to a frame-relay cloud that accesses
multiple remote hubs. One of those remote hubs has another ethernet
interface - say 10.1.0.0 subnet.
The frame relay cloud has a subnet of its own defined between the spoke and
the various hubs. I have configured interface-dlci statements as required
(could also be map statements - no real difference) to establish my partial
mesh between the spoke and the hubs.
Next, I add a static route statement to the SPOKE router like "ip route
10.1.0.0 0.0.255.255 interface serial 0".
Finally , I try to ping from the PC on network 192.168.1.0, and what happens
is that I get "encapsulation failure" for the traffic being routed out
serial 0. This is not surprizing, because the frame relay network has no
idea which dlci to use to route 10.1.0.0 traffic - it only knows the
frame-relay subnet through inverse arp or map statements.
If I replace the dlci statement for the remote hub (that is connected to the
10.1 subnet) with a map statement linking the dlci to the pinged remote
address (such as 10.1.0.1), it works. This shows that - when you route to
an interface, the next hop address used for the output layer 2 is the
destination address. On a true broadcast network, proxy arp kicks in to
reply to arp requests, but Frame Relay has no such facility.
At least I think that is what is happening....
----- Original Message -----
From: "Chuck Church" <cchurch@optonline.net>
To: "Doug Calton" <dcalton@fuse.net>; <ccielab@groupstudy.com>
Sent: Tuesday, December 10, 2002 11:05 AM
Subject: Re: Frame Relay and Policy Routing
> So the problem is the hub router being able to reach the LAN on the other
> side of the 2 MP spoke routers? Does the hub have a route for that
subnet?
> Are you running a routing protocol? Also, you do have different subnets
on
> the two subinterfaces, right?
>
> Chuck Church
> CCIE #8776, MCNE, MCSE
>
>
> ----- Original Message -----
> From: "Doug Calton" <dcalton@fuse.net>
> To: "Chuck Church" <cchurch@optonline.net>; <ccielab@groupstudy.com>
> Sent: Tuesday, December 10, 2002 10:54 AM
> Subject: Re: Frame Relay and Policy Routing
>
>
> > The specific configuration is set up so that there are two
subinterfaces.
> > The first goes to a point-to-point (mandated in the lab) connection to
one
> > remote spoke router. The second subinterface connects via multipoint to
> two
> > other spokes, with all these spoke interfaces sharing the same subnet
with
> > this second subinterface. The target LAN actually connects these two
> other
> > spoke routers on another subnet.
> > In configuring the second subinterface, I can either specify both dlci's
> for
> > the remote spoke routers (interface-dlci) and rely on inarp OR I could
use
> > frame relay map to manually associate the IPs for those remote spokes to
> the
> > DLCIs. Using the latter, I can substitute an address for the target LAN
> to
> > get the request to "work", but of course, I cannot then access that
spoke
> > router directly anymore. Of course, it is not the right solution.
> >
> >
> > ----- Original Message -----
> > From: "Chuck Church" <cchurch@optonline.net>
> > To: "Doug Calton" <dcalton@fuse.net>; <ccielab@groupstudy.com>
> > Sent: Tuesday, December 10, 2002 10:09 AM
> > Subject: Re: Frame Relay and Policy Routing
> >
> >
> > > Doug,
> > >
> > > You've got subinterfaces on the hub router, one of which is a
> > > multipoint. What does the addressing scheme look like and what are
you
> > > trying to ping from/to to test it?
> > >
> > > Chuck Church
> > > CCIE #8776, MCNE, MCSE
> > >
> > >
> > > ----- Original Message -----
> > > From: "Doug Calton" <dcalton@fuse.net>
> > > To: "Chuck Church" <cchurch@optonline.net>; <ccielab@groupstudy.com>
> > > Sent: Tuesday, December 10, 2002 4:15 AM
> > > Subject: Re: Frame Relay and Policy Routing
> > >
> > >
> > > > Thanks - the exercise is very specific as to the placement of the
> > policy,
> > > as
> > > > well as the use of set interface over set next-hop. Oddly, the
target
> > > > subnet is linked to both spokes of the hub, and the exercise has me
> > > shutdown
> > > > the subnet I/F on the non-target IP. Frame maps is all I see, but
it
> > > > targets IP addrs, and not the whole subnet, unfortunately.
> > > > ----- Original Message -----
> > > > From: "Chuck Church" <cchurch@optonline.net>
> > > > To: "Doug Calton" <dcalton@fuse.net>; <ccielab@groupstudy.com>
> > > > Sent: Monday, December 09, 2002 8:21 PM
> > > > Subject: Re: Frame Relay and Policy Routing
> > > >
> > > >
> > > > > Doug,
> > > > >
> > > > > I'm not sure if I'm reading it right, but it sounds like
you're
> > > policy
> > > > > routing on the wrong router. I don't see why policy routing would
> be
> > > > > required at the hub router, as it's got PVCs to all the others,
> right?
> > > > This
> > > > > sounds a lot like one of the bootcamp labs, if I remember right.
If
> > > > router
> > > > > A is your hub, with B and C as spokes, you could policy route on B
> so
> > > that
> > > > > traffic to C, make A the next hop. Same principle is applied to
C.
> > The
> > > > > other way of course would be using frame maps.
> > > > >
> > > > > Chuck Church
> > > > > CCIE #8776, MCNE, MCSE
> > > > >
> > > > >
> > > > > ----- Original Message -----
> > > > > From: "Doug Calton" <dcalton@fuse.net>
> > > > > To: <ccielab@groupstudy.com>
> > > > > Sent: Monday, December 09, 2002 4:40 PM
> > > > > Subject: Frame Relay and Policy Routing
> > > > >
> > > > >
> > > > > > I am working on a training scenario where we are to route
traffic
> > > > destined
> > > > > for
> > > > > > a specific IP subnet through a Frame Relay partially meshed
> network,
> > > by
> > > > > using
> > > > > > the "set interface" command of the route-map subcommand. The
> router
> > > to
> > > > > which
> > > > > > the policy is applied uses subinterfaces, and the subinterface
> that
> > I
> > > am
> > > > > > setting in route-map is a multipoint interface acting as the hub
> to
> > a
> > > > > frame
> > > > > > relay subnet.
> > > > > >
> > > > > > When configured normally, the routing policy works, but the
packet
> > is
> > > > > dropped
> > > > > > because of encapsulation failure leaving the frame relay subint.
> I
> > > can
> > > > > get
> > > > > > the configuration to "work" by configuring a frame-relay map
> > statement
> > > > for
> > > > > a
> > > > > > destination IP address in the target subnet, but this is not an
> > ideal
> > > > > > solution. Is there an more generalized way to encapsulate the
> > exiting
> > > > > traffic
> > > > > > to the appropriate dlci, or possibly another approach to
allowing
> > this
> > > > > traffic
> > > > > > to traverse the frame-relay network? Thanks!
> > > > > > .
> > > > .
.
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