From: Chris Hugo (chrishugo@xxxxxxxxx)
Date: Tue Jul 16 2002 - 17:33:51 GMT-3
Hi,
I realize most folks might not have the Alex Zinin book but since you guys are
discussing a topic I just read through I will post a couple of snippets from hi
s book that I feel might clear the air a little bit.
Page 242-243 and section 5.4.2.3
----start of excerpt----
If you revisit the logic of the forwarding engine in Cisco routers. you can see
that when a packet is routed along a route referencing only an interface, the
packets destination address is used as the next-hop address. This is done just
the same way as when a packet is delivered to a host on a directly connected s
ubnet: The forwarding engine finds the interface route, takes the destination a
ddress as the next hop and passes this information to the packet-delivery proce
dure. The packet delivery code uses ARP or map tables to find data-link details
corresponding to the next hop address. The same process is used when a static
route is configured with INTERFACE ONLY.
Another example of incorrect use of static routes in a Frame Relay environment
was in a point-to-multipoint scenario. The forwarding engine used the destinati
on IP addresses in the packets to look through the Frame Relay map table. As no
matching entry was found--the map statements were configured for the next-hop
addresses corresponding to remote routers, not hosts to remote subnets-- the ma
jority of the packets dropped.
The same problem can show up if static routes referencing only interfaces are u
sed for DDR: The dialer maps contain the address of remote routers, whereas act
ual next-hop address used by the forwarding engine are the destination addresse
s from the packets.
So what is rule of thumb?
Use static routes over interfaces only if the corresponding interface is point-
to-point, that is if encapsulation is HDLC, PPP, or is a point-to-point sub int
. Otherwise, always configure static routes with both the output interface and
the next-hop address.
----end of excerpt----
hth,
chris hugo
Carlos G Mendioroz <tron@huapi.ba.ar> wrote: Yes, it also works. But WHY woul
d you want to do that ?!!!
The static to the interface is bringing in trouble. Use a floating to
the next hop!
Again, I'm missing the reason of your wanting it not to show in the
routing table...
Yakout Esmat wrote:
>
> I don't think it is possible too, I haven't seen any documentation where
> local interface is used on floating static route.
>
> I have no routers to test it at the moment, but will post the results once I
> did that.
>
> -----Original Message-----
> From: kris.keen@aon.com.au [mailto:kris.keen@aon.com.au]
> Sent: Tuesday, July 16, 2002 4:42 PM
> To: Yakout Esmat
> Cc: Groupstudy; nobody@groupstudy.com; Carlos G Mendioroz
> Subject: RE: Default route over ISDN
>
> I would doubt that, if you point a static to a connected interface, does
> the distance default to 0? Can you override admin distance? like this..
> I will mock this up as I'd be intrested to see
>
> -----------------------------------------------------------------
> Kris Keen - CCNP, CCDP, CNE
> Network Support Specialist - Network Systems
> Aon Risk Services Australia Limited
> (612) 9253 7272
> 0404862970
> E: Kris.Keen@aon.com.au
>
> "Yakout Esmat"
> >
> s.com.au> cc: "Groupstudy"
>
> Sent by: bcc:
> nobody@groupst Subject: RE: Default route over
> ISDN
> udy.com
>
> 16/07/2002
> 04:05 PM
> Please respond
> to "Yakout
> Esmat"
>
> I guess this also might work, only if you have another default route
> pointing to different direction, and if this disappears use the floating
> one.
> But not sure that this is possible "ip route 0.0.0.0 0.0.0.0 bri0 200"
>
> -----Original Message-----
> From: Carlos G Mendioroz [mailto:tron@huapi.ba.ar]
> Sent: Tuesday, July 16, 2002 10:53 AM
> To: Yakout Esmat
> Cc: Groupstudy
> Subject: Re: Default route over ISDN
>
> Well,
> as Mas suggested, putting a dialer string works, just tested it.
>
> What I do not understand is your reason for making this an interface
> route.
> If what you want is that the route is hidden, I guess a floating static
> is in order.
>
> Yakout Esmat wrote:
> >
> > Carlos,
> >
> > It makes sense, but if I need to hide the default route from routing
> table,
> > then I have to point to my local bri interface, otherwsie if I point to
> next
> > hop it will be installed in my routing table.
> >
> > What you are saying is that if I point to my interface it doesn't work??
> >
> > -----Original Message-----
> > From: Carlos G Mendioroz [mailto:tron@huapi.ba.ar]
> > Sent: Tuesday, July 16, 2002 3:12 AM
> > To: Yakout esmat
> > Cc: Groupstudy
> > Subject: Re: Default route over ISDN
> >
> > Yakout,
> > when you send a packet to an interface (via ip route 0.0.0.0/0 int x)
> > somehow the interface has to encapsulate it and send it.
> >
> > On DDR interfaces that also accounts for knowing where do you have to
> > dial to. This is "solved" via maps iif you have a destination IP, but
> > in your first case, you don't. Therefore, "encapsulation error".
> >
> > Does this make sense to you ?
> >
> > Yakout esmat wrote:
> > >
> > > Any body aware of this problem..
> > >
> > > Scenario:
> > >
> > > 10.1.1.1/24--[R1]------(192.168.1.0/24)-----[R2]----
> > > ISDN
> > >
> > > 1) R2 is configured with a static default route
> > >
> > > Problem:
> > >
> > > 1) If the default static route on R2 is pointing to BRI0 interface "ip
> > route
> > > 0.0.0.0 0.0.0.0 bri0", R2 can't ping 10.1.1.1 on R1. Getting
> > "encapsulation
> > > failed" error when debuging ip packets, and R2 can't initiate a dial.
> > >
> > > 2) If I cahnge the default to point to next hop instead "ip route
> 0.0.0.0
> > > 0.0.0.0 192.168.1.1", every thing is sweet
> > >
> > > IOS 12.1, legacy ISDN with single dialer map statement is used, IP
> > classless
> > > is on...
> > >
> > > I must be missing some thing.
> > >
> > > Thanks
> > >
> > > Yakout
This archive was generated by hypermail 2.1.4 : Sat Sep 07 2002 - 19:36:32 GMT-3