cisco 7204 substitution

Unanswered Question
Feb 1st, 2009


<p>Hi i'am using 7204 for doing BGP I have reed about the wrowing of routing tables & the 7024'FIB limitation. SO, I have to get something else for doing bgp. </p>

<p>Wath could substitute de 7204 taking in to account that Ihve one BGP secion & will add another one in a few months?</p>

<p>I have catalyst 6500 doing all the switching stuff . If I upgrade the sup engines, say to 720 3BXL,  could I do BGP in the catalyst  and forget about 7204?</p>

<p> </p>


I have this problem too.
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Giuseppe Larosa Sun, 02/01/2009 - 04:43

Hello Osvaldo,

sup 720 3BXL can handle multiple BGP full tables (up to 3).

For example we have two C7609 with sup 720 3BXL each with two BGP sessions receiving full tables in your DMZ.

So you can think of upgrading the C6500 instead of purchasing a new device to perform as border router.

Hope to help



celiocarreto Sun, 02/01/2009 - 09:18


in my opinion you need 256 MB per BGP Session. In order to handle two of them, you can upgrade the memory in the 7204 (depends on NPE) or use the cat 6500.

Regards, Celio

Joseph W. Doherty Sun, 02/01/2009 - 09:37

Similar to Celio's post, I thought the most common limitation for many routers when doing Internet BGP is having sufficient RAM.  You might check whether your existing 7204 supports accepting more RAM and/or whether you can upgrade to a "better" processing engine (especially if it's a VXR).

Although there's nothing wrong with the sup720-3BXL, you often lose some IOS features especially if you don't have WAN cards (which are more limited in the 6500 vs. the 7600).  So, you might consider replacement router such as the 7201 or perhaps a 3800 series ISR, depending on the performance you need  (the 3800 ISR offer similar or better performance compared to the early 7200 NPEs).

languedoc Sun, 02/01/2009 - 13:41


so you say that wath is important for BGP is the memory and not the FIB size. So wath is the function of FIB?.

I have 7204 VXR if I go with sup 720 3BXL waht IOS function do I lose?



Joseph W. Doherty Sun, 02/01/2009 - 16:45

The FIB (forwarding information base) is, I believe, is built from the routing table and is used to make forwarding packet decisions.

What IOS functions you might lose depend on the IOS version and features sets between your 7200 and the 6500, and with the latter, what hardware's installed.  If you're only doing basic routing, good chance the two will be very similar.

languedoc Mon, 02/02/2009 - 01:39


the FIB is used to make forwarding packet decisions, if it is limited in size as is the case in 7204. How could increasing the memory help? If increasing memory bypass the FIB limitation.

Wath is the truth about forwarding packets decition in BGP??

Joseph W. Doherty Mon, 02/02/2009 - 03:59

Did you notice "FIB/TCAM size limit on a Sup1A/MSFC2" in your reference? The Sup1A/MSFC2 is used in a 6500, i.e. this isn't about 7200s. TCAM sized it tied to the 6500/7600 supervisor.

languedoc Sun, 02/01/2009 - 16:55


in this forum

they talk about filtering bgp if a default route is received..........How you would have to handle this situation today is to apply an inbound filter on your BGP sessions with your upstream providers that just tosses out some selective routes to get you under the 256k limit. In practice, it generally works best to just chop out the smaller network advertisements (/24 or /25 and longer masks) -- i.e. "permit le 23". To do this and not cause an reachability isssue with the networks you've filtered from your table, you MUST also take a default route from at *least* one of your upstream carriers as a catch-all. This will allow you to retain most of the benefits of taking full tables from your upstreams for TE purposes, but keep you from nuking your boxes in the process.....

but how do I know if I receive a default route from my peer?  in any case I added a route pointing to my peer.


your ideas please!!




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