Load Balancing and Failover on Perimiter Routers?

[mRgEE]

Hi,

I have a requirement for 2 seperate Internet connections from 2 different ISPs to my network.
This is to provide redundancy in the case of one failure. I would like to load balance these connections and configure the routers for failover should one go down.
Is this configuration possible? I have 2 spare sets of cisco 3600 and 4000 routers available.

 

[UnaBomber]

Yes its possible, Is this for a WAN configuration, to another Site, or just for access to the

http://WWW (multi-homed)?

If

http://WWW you

can use BGP or static floating routes

If WAN you can use HSRP and track a tunnel to another IP address on the other side of the WAN.

Both will give you redundancy and with a little tweaking you can get BGP and Static Routes to load share. HSRP you cant

UnaBomber
ccnp mcse2k

 

[mRgEE]

This is for

http://WWW traffic

and not specific site to site.
Basically I will have various customers connecting to my network via the Internet using SSL. I need to ensure that should one ISP Internet connection become unavailable then the other can be used as failover. Ideally I want to load balance the traffic so as not to have one connection sat not being utilized.
As yet I have not purchased any service and am looking into whether leased lines or high speed Business ADSL will be utilized for the connection.

 

[KiscoKid]

BGP is arguably the way forward for you. The following link from Cisco expains how to setup load sharing using this protocol:

http://www.cisco.com/en/US/partner/...iguration_example09186a00800945bf.shtml#conf4

 

[helpdeskdan]

Does not one require permission from their ISP to use BGP?

Also, how can one load balance with static routes? Half the addresses use one, half the other I assume? If there's a better way, I'd be quite curious to know.

 

[UnaBomber]

Also, how can one load balance with static routes? Half the addresses use one, half the other I assume? If there's a better way, I'd be quite curious to know

Yeap, you could do that, you can also load share across equal paths with static routes IIRC.

Anyway he needs load balancing inbound sessions, which is a whole different thing, BGP is the way forward, and yes you will have to get your Telco involved



UnaBomber
ccnp mcse2k

 

[helpdeskdan]

Pardon? Static routes IIRC? I have never heard of this, might you have a link? Thkx

 

[UnaBomber]

IIRC = If I Recall Correctly

http://www.tek-tips.com/faqs.cfm?fid=387

http://www.cisco.com/univercd/cc/td...122cgcr/fipr_c/ipcprt2/1cfindep.htm#wp1025915

Static routes will install 6 parallel routes to a destination, you can change it using the

maximum-paths maximum

UnaBomber
ccnp mcse2k

 

[plshlpme]

pbr is also another option...

http://www.cisco.com/warp/public/732/Tech/plicy_wp.htm

http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/qos_c/qcpart1/qcpolicy.htm

 

[helpdeskdan]

And here I thought there was a new kind of static route! Obviously, I'm rusty on my abbreviations.

There's Cisco Optimized Edge Routing:

http://www.cisco.com/en/US/netsol/ns471/netqa0900aecd800f5584.html

http://www.cisco.com/en/US/netsol/ns471/networking_solutions_white_paper0900aecd80243f70.shtml

Now, as for maximum paths, that's a routing protocol command. I believe you may find that won't work for static/default routes.

http://cco.cisco.com/en/US/products...erence_chapter09186a008017d029.html#wp1058523

Feel free to prove me wrong on this - I am curious to find a load sharing/default route/non bgp answer.

As to the actual question, load balancing inbound traffic, I'm a bit confused - BGP will not load share to two different ISP's. BGP can only pick the best route.

http://www.cisco.com/warp/public/459/40.html#conf4

Perhaps I have missed something?

 

[UnaBomber]

Dont know what to say to you, if you dont bother to read links I post, then I am unsure how on earth I am going to *prove* something to you.

Anyway I will attempt to theorise a concept for you, but you could just prove this to yourself on a router...

Are you aware that you can create 2 Static routes to the same destination via difference Next hops or interfaces, AND change the administrative distance so you create what we term a Floating route?

If you are aware of this then you will also logically conclude that it is possible to enter 2 difference routes to the same destination into the routing table via Statics. What if I was to leave the administrative distance alone? That would cause both paths to be equally preferred, and in fact a Cisco Router will load balance across these paths up to the default 6 paths or whatever you choose as the maximum paths.

http://tcpmag.com/qanda/article.asp?EditorialsID=259

From a ubber geek quadruple ccie

UnaBomber
ccnp mcse2k

 

[helpdeskdan]

Please forgive my ignorance; I am new! I seek to prove nothing, I seek only to obtain knowledge through the process of finding information to disprove my theories. Poorly worded textbooks lead me to believe that load balancing was a function of routing protocol instead of being inherent to the routing process. In other words, static routes can be load balanced. Incorrect documentation lead me to believe maximum-paths was exclusively a routing protocol command. It can be entered in router configuration mode. Default routes also can be load balanced as long as one uses ip route 0.0.0.0 0.0.0.0 statements and not ip default network. (ip default network always takes precedence. IGRP is notorious for needing this command as it does not understand routes to 0.0.0.0)

I do find it odd that multiple default routes are never listed as an alternate means of multihoming. Nowhere have I seen this done by any means but by BGP. The link previously given states BGP will load share, but not load balance between two ISP's hence one would think it would be more popular. I do not question that two default routes can be, as I have read nothing to disprove it, but I am curious as to why it is never listed as an alternate BGP solution?

 

[KiscoKid]

Using static routes come with a couple of disadvantages in this scenario:

First thing to consider, they are not aware of upstream failure thus the router may continue to send packets to its peer when in fact the peer is no longer there. Admittedly this can be mitigated somewhat by using a connected route which work well in situations where the line status changes. But consider that that not all WAN transmission medium failure results in a change in interface status (frame relay is a classic example). In addition, you may have a more remote failure rather than between your router and the one it peers with. For example, an ISP's main peering router may go down and stop participating in BGP. Thus any of its customer peering routers will become aware of this failure as they will also lose these routes. But in a static routing environment, your router will continue to send traffic to the ISP neighbor even tho this ISP router has lost all its BGP routes from its upstream peer and may not have an alternative route - in a properly-designed ISP network however this should never be the case.

All that said, Cisco are continually improving on the traditional ideas. Now they allow you to "monitor" a remote node and to use a static route to that node if it available. If that node disappears, the router can be made to fallback to a different static route. Cisco call it "reliable static routing" and it uses ICMP echo's to determine the status of a remote node. Albeit this is not infallible as I once had a situation where an ISP introduced a firewall between my router and the node I was polling. This firewall didn't allow ICMP pings which made things interesting for awhile!

Second thing to consider, static routing may introduce a significant administrative overhead regarding having to update your routing whenever the network is changed, expanded etc.

 

[UnaBomber]

I agree with your assessment. For load balancing across two internet connections, outbound, for a small company statics would do fine.

But if you are hosting services, you need to look at this from a different angle.

Using BGP with 2 different ISP will not however Load Balance, BGP only inserts 1 path into its routing table so you will never be able to have >1 equal cost path, thus no load balancing. BGP picks the best route to a destination via the best fitting prefix and shortest AS Path.

You can configure Load Sharing via BGP tweaking different BGP attributes. Using BGP Multipath one can have more than 1 path to the same destination installed, however the router will only allow one to be the best, according to the BGP Best Path Selection Algorithm and will advertise this route.

http://www.cisco.com/warp/public/459/25.shtml#bgpmpath

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122t/122t11/ft11bmpl.htm

http://www.cisco.com/warp/public/459/40.html

UnaBomber
ccnp mcse2k