From: Baety Wayne SrA 18 CS/SCBX (Wayne.Baety@kadena.af.mil)
Date: Thu Oct 03 2002 - 05:03:07 GMT-3
Answers inline (bracketed)....
WAYNE A. BAETY, SRA, MCSE, USAF
18th Communications Squadron
DSN: 634-9927
Commercial: 011 81 611 734 9927
-----Original Message-----
From: Hunt Lee [mailto:huntl@webcentral.com.au]
Sent: Thursday, October 03, 2002 3:51 PM
To: 'Bruce Williams'
Cc: 'Young K. Bae'; 'Chris Hugo'; 'Donny MATEO'; 'Baety Wayne SrA 18
CS/SCBX'; 'folivore'
Subject: RE: What if OSPF routes have shorter masks than RIP?
Hello,
I have read through the entire thread for 3 times already. However, I'm
still not so clear on what are the 4 solutions that Wayne proposed, can
someone please kindly explain to me??
1st Solution:
On both the interfaces connecting between R1 & R2, use a secondary IP from
the 172.16.0.x/25 network, so the RIP network will have the same subnet mask
as OSPF network (this I understand)
2nd Solution:
[[[[[[[[[[
Read solution 3 carefully and understand the principles before reading this.
RIP will automatically translate all subnet advertisements received from one
classful network into a single advertisement containing only that classful
network when advertised to another classful network. It is sorta like
aggregating an address with BGP, except you have no control over the
aggregation.
For instance, when 172.16.200.0/25 is advertised from one router unto a RIP
enabled interface of another router that has an address like 172.17.201.1/25
since 172.16 is a different classful network thatn 172.17, all subnets
pertaining to 172.16/16 (including 172.16.200.0/25) will be pruned from the
update and replaced with a single advertisement of 172.16.0.0/16. This is
called a subnet default route. You can use this feature of RIP to your
advantage by using a different classful network prefix in your RIP domain
than your OSPF domain. Your OSPF domain will send this subnet default route
to your RIP domain, and your RIP domain will maintain reachability to that
classful network.
-Wayne
]]]]]]]]]]
Assign it with a completely different classful (or classless??) network for
the RIP domain
e.g. 192.168.1.0 /24
Problem 1) I have tried to set the RIP network as a Classful network
(192.168.1.0/24) & classless network (192.168.1.0 /28) & they both work...
so isn't sure what Wayne means by using a "classful network altogether"
Problem 2) I tried to turn on / off RIP's auto-summarization by "no
auto-summary" / "auto-summry" under RIP process and once again, they both
work too... so again wasn't sure what Wayne means by "relying on
auto-summarization & advertisement of the classful network"
3rd Solution:
[[[[[[[[[[[
Your ospf domain had the network 172.16.200.0/25 advertised, yet your RIP
domain only understands /26 sized subnets of 172.16/16, other classful
networks (e.g. 172.17/16, 172.18/16, etc), and the default route (0.0.0.0).
Translate 172.16.200.0/25 into 2 different sized /26 subnets and your RIP
domain will then understand it.
This could be accomplished with this....
(Example 1)
ip route 172.16.200.0 255.255.255.192 eth0
ip route 172.16.200.64 255.255.255.192 eth0
Or This...
(Example 2)
ip route 172.16.200.0 255.255.255.192 [next-hop ip address]
ip route 172.16.200.64 255.255.255.192 [next-hop ip address]
However, as you have stated you cannot use static routes. Therefore slap
those networks on an interface in your OSPF domain as secondaries. It will
have the same effect as making a static to an interface as shown in Example
#1. This will make those nextworks appear to your routing process as being
directly connected. That means your router will ARP for those networks as
though they appeared on the connected medium. However, you've already
defined that network somewhere else in your OSPF domain as 172.16.200.0/25.
What will happen is that the router where on these statics are applied
(example 1 style only) will send an ARP broadcast over the medium for any
packets it receives falling within that range. Another router that sees
these ARP broadcasts and has proxy-arp turned on will respond to these ARP
broadcasts with its own interface address and offer to forward those packets
to their correct destination. This is called proxy ARPing and that's why
you would need proxy-arp turned on.
-Wayne
]]]]]]]]]]
"He could also subdivide the smaller size prefix with secondary networks
into multiple networks that match the larger subnet size of the RIP domain
(3rd Solution). To get this into the routing table static addressing would
be the the preferred method but using secondaries on one of the router links
in the OSPF domain and relying on proxy-arp to determine destination
next-hop would also work."
I'm completely loss =( not sure wot Wayne is referring to here?!? What
are the smaller size prefix / larger subnet size of RIP domain??? And what
static addressing is Wayne referring to?
4th Solution:
[[[[[[[[[[
Solution 4 is exactly like solution 1 except you use a tunnel connection to
interconnect your routers thereby avoiding the necessity to "pathing" your
routing information throughout your network.
Once you research and understand how to work with just creating simple
tunnel interfaces, you'll know what we mean. You'll get an a-ha.
]]]]]]]]]]
"A 4th Solution (that was mentioned) is to create a tunneled interface
matching the subnet size of the RIP domain with the endpoint of the tunnel
running to each RIP router requiring reachability information about that
subnet size."
I haven't used any Tunnel interface before. Can someone kindly give me some
e.g. here? How would I do it for Young's e.g.?
Thanks.
Best Regards,
H.
-----Original Message-----
From: Bruce Williams [mailto:bwilliams175@comcast.net]
Sent: Wednesday, 2 October 2002 1:31 PM
To: Donny MATEO
Cc: ccielab@groupstudy.com
Subject: RE: What if OSPF routes have shorter masks than RIP?
Split Horizon should be disabled on the interface that has the secondary
address so that both networks can be advertised out the interface.
Check out this link on secondary addresses and split horizon.
http://www.cisco.com/warp/public/105/41.html
Bruce
-----Original Message-----
From: Donny MATEO [mailto:donny.mateo@sg.ca-indosuez.com]
Sent: Tuesday, October 01, 2002 11:12 PM
To: Bruce Williams
Cc: ccielab@groupstudy.com
Subject: RE: What if OSPF routes have shorter masks than RIP?
Could you be more specific on which issue. If it's a routing feedback from
the other router, for most interface split-horizon is enabled. The only
execption i know and had accountered so far is the physical serial interface
for frame-relay. Do let me know if you found other issues. I'll try to lab
it again tonight.
Donny
Bruce Williams
<bwilliams175@com To: Donny MATEO
<donny.mateo@sg.ca-indosuez.com>, Richard Davidson
cast.net> <rich@myhomemail.net>
Sent by: cc:
ccielab@groupstudy.com
nobody@groupstudy Subject: RE: What if OSPF
routes have shorter masks than RIP?
.com
02-10-2002 10:37
Please respond to
Bruce Williams
If you use secondary addresses, how do you deal with the split horizon
issue?
Bruce
-----Original Message-----
From: Baety Wayne SrA 18 CS/SCBX [mailto:Wayne.Baety@kadena.af.mil]
Sent: Wednesday, 2 October 2002 12:55 PM
To: 'folivore'; Baety Wayne SrA 18 CS/SCBX; 'Young K. Bae';
ccielab@groupstudy.com
Subject: RE: What if OSPF routes have shorter masks than RIP?
So far 4 solutions that work...
Yes, what you've stated is called tunnelling the subnet with secondaries
(1st Solution). That would work in this instance because there is only 1
router in his diagram involved on the RIP side. It's viable as long as he
remembers to place a secondary network throughout his RIP domain on each
router link (sorta like creating a path) to maintain connectivity and
reachability information about that particular subnet size. (RIP silently
drops information about subnets across subnets with a differing subnet size
but part of the same classful network). It may be better to use a different
classful network altogether (2nd Solution) and rely on auto-summarization
and advertisement of the classful network. He could also subdivide the
smaller size prefix with secondary networks into multiple networks that
match the larger subnet size of the RIP domain (3rd Solution). To get this
into the routing table static addressing would be the the preferred method
but using secondaries on one of the router links in the OSPF domain and
relying on proxy-arp to determine destination next-hop would also work.
Solution 2 and 3 require modification of relatively a few routers and
probably can be more easily documented than Solution 1. A 4th Solution
(that was mentioned) is to create a tunneled interface matching the subnet
size of the RIP domain with the endpoint of the tunnel running to each RIP
router requiring reachability information about that subnet size. This is
really just Solution 1 with performance drawbacks for the sake of
convenience and possibly smaller subnet utilization (if every router doesn't
require reachability information). Both Solution 1 and 4 require
provisioning a new subnet for each router link just for the sake of carrying
information about subnets that have a different subnet size in the routing
table: something that can be quite wasteful if deployed in a large scale
fashion.
WAYNE A. BAETY, SRA, MCSE, USAF
18th Communications Squadron
DSN: 634-9927
Commercial: 011 81 611 734 9927
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of Donny
MATEO
Sent: Tuesday, October 01, 2002 10:04 PM
To: Richard Davidson
Cc: ccielab@groupstudy.com; nobody@groupstudy.com
Subject: RE: What if OSPF routes have shorter masks than RIP?
I've tried this and yes it works.
Care have to be taken though, I was testing on different IOS version and
guess what...they all got different behaviour. Some works some don't. So, it
all depends on which IOS you are using.
Donny
Richard Davidson
<rich@myhomemail. To:
ccielab@groupstudy.com
net> cc:
Sent by: Subject: RE: What if OSPF
routes have shorter masks than RIP?
nobody@groupstudy
.com
28-09-2002 11:11
Please respond to
Richard Davidson
Would a secondary addresses on R2 and R1 in the range of 172.16.100.9/29
work? Please let me know if it does. Rich "Young K. Bae" wrote:Hi Bob,
The solution stated in the document requires static routes, which I'm not
allowed to do. Is there any other way to accomplish the object without using
static routes?
Thanks,
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> Bob Sinclair
> Sent: Friday, September 27, 2002 7:17 PM
> To: Young K. Bae; ccielab@groupstudy.com
> Subject: Re: What if OSPF routes have shorter masks than RIP?
>
>
> Try this link:
>
> http://www.cisco.com/warp/public/105/52.html
>
> It is ugly!
>
> ----- Original Message -----
> From: "Young K. Bae"
> To:
> Sent: Friday, September 27, 2002 8:51 PM
> 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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