Asymmetric Routing using router

Hi, Need some info , how to do the asymmetric routing with 2 different ISP as upstream provider. We have our own IP pool and own ASN from APNIC.

We have /18 IP pool. Wants to route /19 thru one ISP ( 20 Mbps) and other /19 thru another ISP(10 Mbps).

Both shopuld acts as backup to each others.

Thanks in advance.

Kind Regards, SD

Reply to
SarojDey
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Hi,

For incoming traffic towards your addresses technically it's nothing special - just configure BGP to advertise prefixes in such way that given prefix gets better preference over selected provider, while other gets lower (in simplest scenario AS_PATH, more sophisticated would using communities - check with your upstreams what communities they support). However there might be serious administrative problem - if default allocation size in major /8 block where you got your addresses from is more than /19 you some networks may filter your announces at their discretion. Fortunately /19 is rather big and I don't recall any default allocation being bigger than this. So you should be ok here (but check).

For outgoing traffic you have choice between: - simply using best AS_PATH through whichever ISP it happens to be and hope traffic will be about equal on each link - adjust local-pref of selected incoming announces in such way that traffic moves over whichever link you choose - disregard any incoming announce and use policy-based routing (PBR) to send traffic over the link which is primary for given /19 of the source IP (and backup over second if it fails)

While last option may look attractive it usually won't produce best performance both due to PBR and likely sub-optimum path to destination. First option looks ok, but chances to get optimum balance of traffic are not very high (depends on your traffic patterns and providers of course). So the middle option seems to be the best choice but it requires a lot of work analysing traffic patterns, tweaking local-pref, then repeat it until you get desired optimum. Quite common to choose routing to/from some part of the world via one provider, while to/from another part of the world via another. Though this assumes that providers are either about equal or have best connectivity to choosen part of the world better than to another.

As for backup - as long as you advertise you prefixes over both links (just with different attributes) and have either full-bgp or partial+default routes on both links BGP will do backup automagically.

Is this what you're looking for?

Kind regards, iLya

Reply to
Charlie Root

in terms of configuration it would look something like

router bgp neighbor remote-as 2 neighbor route-map AS-2-OUTBOUND out neighbor remote-as 3 neighbor route-map AS-3-OUTBOUND out exit

route-map AS-2-OUTBOUND permit 10 match ip address prefix-list BLOCK-2 set as-path prepend

route-map AS-3-OUTBOUND permit 10 match ip address prefix-list BLOCK-1 set as-path prepend

ip prefix-list BLOCK-1 description 1st /19 block ip prefix-list BLOCK-1 permit x.x.x.x/19

ip prefix-list BLOCK-2 description 2nd /19 block ip prefix-list BLOCK-2 permit y.y.y.y/19

Reply to
Merv

Exactly this is wht i wants to achieve. Main intention is to pass on the dedicated bw customer thru one link ( ISP) and shared customer thru the other link (ISP). So the incomming traffic and out going traffic should take the intended route. No load balance is required. Or else shared customer will take route of dedicated Link.

But if one link is down, the other can be used as backup.

Will appreciate if you can suggest brief config too.

Thanks ! Kind Regards, SD

Reply to
SarojDey

That's the exact *opposite* of asymmetric routing. Asymmetric means that the inbound and outbound paths are different, but you want them to be the same.

Reply to
Barry Margolin

I understand this is opposite of asymmetric routing. This is the initial setup. After this i will have another ISP connected , which will only provide incomming traffic to me. And another link will take care of outgoing traffic.

I feel this point it will make more complex. So i wants to acieve the following first.

Can i have some :***advice about the configration in my router ***

Exactly this is wht i wants to achieve. Main intention is to pass on the dedicated bw customer thru one link ( ISP) and shared customer thru

the other link (ISP). So the incomming traffic and out going traffic should take the intended

route. No load balance is required. Or else shared customer will take route of dedicated Link.

But if one link is down, the other can be used as backup.

Both the ISP will be connected to 2 different iterface of a single Router.

Will appreciate if you can suggest brief config too.

Thanks ! Kind Regards, SD

Reply to
SD

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