Re: [isp-bgp] BGP Multihoming tips

[vdadlaney@...]

Hi Praful,

The setup you have means that you are using ISP 2 for backup only. Is that what u had originally intended or were the requirements changed due to some other factors. Just would like to know the thinking behind it in case i have to deal with this in the future. Thx


> Hey all,
> 
> Thanx for the replies. I have setup BGP multihoming
> with ISP1 and ISP2 now. I am accepting provider routes
> only and not the full routing table. I am pushing all
> my outbound traffic to my preferred ISP1 using local
> preference. For routes that are not in my routing
> table, I have a default pointing to ISP1(lesser
> administrative distance) and another default to ISP2
> with higher admin distance.For inbound traffic towards
> my AS, I am using AS-PATH prepend attribute so that I
> prepend my AS 3 times towards ISP2.So when I check the
> reachability to my AS on the route-servers,I see my 
> network reachable via ISP1( because of shorter
> AS-PATH).
> 
> I have checked the reachability from Sprint and Level3
> looking glass. Earlier without the AS-PATH prepend,
> Sprint chose ISP1 to reach my AS, whereas Level3 chose
> ISP2. But now everything is coming in via ISP1.Thats
> what I needed. Any fine tuning required, let me know
> 
> Vikram, when I check out for my 16x.x.x.x/24 network
> in the looking glass, I see BGP entry for the /24
> space and not the aggregate. So  I guess this suggests
> my network is advertised out by ISP1 and ISP2 as /24.
> 
> Thanx 
> Praful
> 
> --- vdadlaney@... wrote:
> > Hi Praful,
> > 
> > Since you have PA(Provider Assigned) address space
> > you would have to negotiate with one of your
> > providers to advertise the more specific subnet
> > since your address block is most probably part of an
> > aggregate. This would give u backup but if you want
> > to do loadsharing like u have mentioned than u would
> > have to get both your providers to announce the more
> > specific block for your subnet. (Depending on the
> > provider they may do this.) This takes care of
> > inbound loadsharing. As far as outbound loadsharing
> > goes you could ask your ISPs for partial routes for
> > their locally originated prefixes and have default
> > routes configured for prefixes that lie beyond your
> > directly connected ISP's. Apologize if my answer is
> > incorrect and would appreciate it if someone could
> > correct me if i am wrong. Thx
> > Regards,
> > 
> > Vikram
> > 
> > 
> > > Hi All,
> > > 
> > > I currently have to setup a network involving BGP
> > > multihoming to two different ISPs. I have a /24 IP
> > > space from ISP1 now.I would like to use it for my
> > > network involving DMZ.I have two Cisco 7200
> > routers
> > > which will run IBGP between them and the ISP1
> > > terminates on R1 and ISP2 on R2 running EBGP. I
> > want
> > > to have inbound and outbound traffic load shared
> > > between the ISPs and redundancy when one ISP
> > fails.
> > > Suggest me some good BGP multihoming tuning tips
> > and
> > > what do I need to negotiate with my ISPs for
> > better
> > > reachability of my network in the internet ?
> > > 
> > > Since I have the PA ( Provider Assigned)  /24
> > space
> > > from ISP1 , how do I go forward with ISP2 to
> > advertise
> > > it . The two ISPs are peered directly.
> > > 
> > > Thank You
> > > Praful
> > > 
> > > 
> > > 
> > > 	
> > > 	
> > > 		
> > >
> >
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