Date: Sun, 31 Dec 2000 18:31:52 +0100 From: Jesper Skriver <jesper@skriver.dk> To: Vincent Poy <vince@oahu.WURLDLINK.NET> Cc: Jeroen Ruigrok/Asmodai <asmodai@wxs.nl>, Christian Kratzer <ck@toplink.net>, Warren Welch <wwlists@intraceptives.com.au>, freebsd-isp@FreeBSD.ORG Subject: Re: Dynamic routing reference sites Message-ID: <20001231183152.A68613@skriver.dk> In-Reply-To: <Pine.BSF.4.31.0012301548120.2027-100000@oahu.WURLDLINK.NET>; from vince@oahu.WURLDLINK.NET on Sat, Dec 30, 2000 at 03:52:59PM -1000 References: <20001230151543.A27587@skriver.dk> <Pine.BSF.4.31.0012301548120.2027-100000@oahu.WURLDLINK.NET>
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On Sat, Dec 30, 2000 at 03:52:59PM -1000, Vincent Poy wrote:
> On Sat, 30 Dec 2000, Jesper Skriver wrote:
> > A Cisco router carrying full routing today really need 256 MB of memory,
> > it can just be in 128 MB of memory, but that's VERY tight.
>
> Yeah but what I mean is that's probably with very few peers. What
> happened if you had like a lot of peers?
-- quote --
How Much Memory Does Each BGP Route Consume?
Each Border Gateway Protocol (BGP) entry takes about 240 bytes of memory
in the BGP table and another 240 bytes in the IP routing table. Each BGP
path takes about 110 bytes.
Under normal circumstances, memory utilization depends on the following
three factors:
number of prefixes (240 bytes per prefix)
number of routes (240 bytes per route)
number of alternate paths (110 bytes per alternate path)
As an example, let's say you're receiving 50,000 prefixes from four BGP
neighbors, and all of them make it into the routing table:
BGP table: 50000 * 240 = 12,000,000 bytes
Routing table: 50000 * 240 = 12,000,000 bytes
Alternate paths: 50000 * 110 * 4 = 22,000,000 bytes
In this case, you'll need approximately 46 MB of RAM, not counting the
RAM needed to support Cisco IOS Software, Interior Gateway Protocols (IGPs),
and so on.
-- unquote --
The above is over estimated as not all routes will have different AS
paths, the below is from a router taking 4 full views + some partial
views.
BGP table version is 34619196, main routing table version 34619196
115916 network entries and 345514 paths using 23334608 bytes of memory
75815 BGP path attribute entries using 3639120 bytes of memory
471 BGP rrinfo entries using 11304 bytes of memory
60418 BGP AS-PATH entries using 1502272 bytes of memory
379 BGP community entries using 10516 bytes of memory
98416 BGP route-map cache entries using 1574656 bytes of memory
Dampening enabled. 290 history paths, 72 dampened paths
BGP activity 794102/678186 prefixes, 23640513/23294999 paths
> And a question, on a Cisco
> router, does the following basically do the route announcements?
>
> router bgp <your ASN>
> bgp dampening
BGP dampning has nothing to do with announcing routes, go read the
documentation, it's public available.
> network x.x.x.x
>
> So basically it will announce the network x.x.x.x to the upstream
> provider with my ASN on it and then the upstream will automatically add
> their AS to it when it announces up another level?
Yes, this is how BGP works.
/Jesper
--
Jesper Skriver, jesper(at)skriver(dot)dk - CCIE #5456
Work: Network manager @ AS3292 (Tele Danmark DataNetworks)
Private: Geek @ AS2109 (A much smaller network ;-)
One Unix to rule them all, One Resolver to find them,
One IP to bring them all and in the zone to bind them.
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