From: folivore (folivore@hotmail.com)
Date: Tue Oct 01 2002 - 13:46:55 GMT-3
For the original diagram, the easiest way is to configure a 172.16.x.0/25
network as secondary IP on whatever interface between R1 and R2, and use
neighbor command in RIP on this secondary IP.
----- Original Message -----
From: "Baety Wayne SrA 18 CS/SCBX" <Wayne.Baety@kadena.af.mil>
To: "'Young K. Bae'" <ybae@cisco.com>; <ccielab@groupstudy.com>
Sent: Monday, September 30, 2002 11:24 PM
Subject: RE: What if OSPF routes have shorter masks than RIP?
> Non 'ip route' method (relies on proxy-arp or auto summarization)
>
> Choose multiple secondary networks that complete the /25.
>
> Put the secondary addresses on an OSPF enabled interface. Make sure it's
a
> real interface involved with packet forwarding (i.e. not a loopback
> interface) otherwise you will kitchen sink packets destined for the more
> specific routes.
>
> Turn Proxy-ARP on for all OSPF routers that could route the more specific
> /26's and that are directly connected to the advertising OSPF router (Any
> router advertising the /25 LSA) (This step can be ignored if you're
dealing
> with a classful routing protocol that auto summarizes and you use two
> address ranges that cross a classful boundary).
>
> Do not insert the /26's into your OSPF domain.
>
> Inject the /26's into your RIP domain.
>
> OSPF (/25)-----Any-------RIP (/26)
> /26 OSPF <-- /26
> /26 Router <-- /26
>
>
> There are two problems with this. The first, is that you will have to
> choose an ip address that is not being used anywhere else in your network
to
> use for the secondaries (the normal ip address conflict detection code
will
> not work). Whatever you choose would need to be heavily documented.
>
> I tested this by using three routers.
>
> Lo1 (/25:1)
> |
> |
> A----------B---------C
> /25:2 /26:3
> /26:1a
> /26:1b
>
> Router A answered ARP packets for addresses within the range of /26:1a and
> /26:1b because it had /25:1 in its routing table. Also, Router B
summarized
> the /26's into a /24 before advertising it to Router C since you will be
> crossing a classful boundary. However, this technique will also work for
> classless routing protocols even without relying on the auto
summarization.
>
> Because /26:1a and /26:1b was in the routing table Router B was able to
> advertise them to Router C via RIP.
>
> Router C was able to ping the Loopback on Router A (and get replies)
because
> /26:3 was in the OSPF domain and /26:1a and /26:1b was in the RIP domain.
>
> The second problem with this method is that Router B will be ARPing for
all
> addresses in the /26:1a and /26:1b ranges and therefore would need to
> increase it's arp cache size if the proxy addresses become significant in
> number.
>
> But since you are dealing with a classful protocol that automatically
> summarizes subnets when crossing classful boundaries, you don't even need
> the secondaries (just choose an addressing scheme that would fit the
> results). This would probably be the answer that a testing proctor would
> want you to come up with.
>
>
> WAYNE A. BAETY, SRA, MCSE, USAF
> 18th Communications Squadron
> DSN: 634-9927
> Commercial: 011 81 611 734 9927
>
>
>
> -----Original Message-----
> From: Young K. Bae [mailto:ybae@cisco.com]
> Sent: Saturday, September 28, 2002 9:51 AM
> To: ccielab@groupstudy.com
> Subject: What if OSPF routes have shorter masks than RIP?
>
>
> Guys,
>
> I'm sure this question has been asked many times before, but can someone
> kindly explain to me again? There are some /25 routes in OSPF Area0 that
I
> need to redistribute into RIP v1. The serial link that connects R1 with
R2
> has a /26 mask. How can I inject /25 OSPF routes into a classful routing
> domain in a case such as this?
>
> R1 --- 172.16.12.0/26 (RIPv1) --- R2 ---- 172.16.100.0/29 (Area1) --- R5
> 172.16.200.0/25 (Area0)
>
> Thanks in advance,
>
> Young
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