Date: Mon, 18 Feb 2008 17:33:07 -0500 From: Bill Moran <wmoran@collaborativefusion.com> To: Tom Judge <tom@tomjudge.com> Cc: Nick Barnes <Nick.Barnes@pobox.com>, freebsd-net@freebsd.org Subject: Re: Multiple default routes on multihome host Message-ID: <20080218173307.00cb1296.wmoran@collaborativefusion.com> In-Reply-To: <47BA037A.8010405@tomjudge.com> References: <38308.1203368454@thrush.ravenbrook.com> <20080218163618.5e6672d3.wmoran@collaborativefusion.com> <6xiZ7xvVdDqVhj0EdhE90pfdIcQ@S1JitD8kpKQ9sTxL7Qyzy/kv7rU> <20080218170642.e079540d.wmoran@collaborativefusion.com> <47BA037A.8010405@tomjudge.com>
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In response to Tom Judge <tom@tomjudge.com>: > Bill Moran wrote: > > In response to Eygene Ryabinkin <rea-fbsd@codelabs.ru>: > > > >> Bill, > >> > >> Mon, Feb 18, 2008 at 04:36:18PM -0500, Bill Moran wrote: > >>> I would suggest you ask yourself (and possibly the list) _why_ you think > >>> multiple default routes is necessary ... what is it that you're hoping > >>> to accomplish. I'm guessing your looking for some sort of redundancy, > >>> in which case something like CARP or RIP is liable to be the correct > >>> solution. > >> I had faced such situation once: I had multihomed host that was > >> running Apache daemon that was announced via two DNS names that > >> were corresponding to two different IPs, going via two different > >> providers. When the first provider's link goes down, the second > >> provider is still alive, and when both providers are alive, the > >> traffic is balanced via DNS round-robin alias. Do you see some > >> better way to do it via CARP, RIP, something different? I am still > >> interested in other possibilities. > > > > The canonical way to do this is with BGP. I can be done with CARP > > if both providers support it and are willing to work together. > > Unfortunately businesses tend to get bundled PA address space when > purchasing leased lines off of ISP. This means that a some what simple > transition from provider A to provider B can not be done with BGP. Also > as the OP states one the the address blocks that he has is a /25 which > most ISP's will filter from the BGP address table because it is to small. You're confusing issues. The OP is in the process of a migration, in which case the packet rewriting via pf/ipfw/etc is probably the best approach. Eygene is describing a different scenario with a permanent multihomed system, in which case BGP is probably the best option, but CARP _may_ be an option. > I think the cost of learning BGP, getting an AS number and a suitable > large block of PI address space, getting 2 routers that can do BGP, > coupled with the consultancy costs charged by the ISP to setup the BGP > feed totally out way the cost of just multihoming a box for a few > days/weeks while the required changes take affect.. Ok so this is not > ideal but hey it works and its simpler.. Agreed. In fact, if you read the prior messages, I never disagreed. Personally, I prefer to do this type of migration as a "flag day" where everything just gets switched over all at once ... but that's not always possible. The OP seems to have a number of systems with public IPs, and it's harder to do a flag day with a lot of systems. -- Bill Moran Collaborative Fusion Inc. http://people.collaborativefusion.com/~wmoran/ wmoran@collaborativefusion.com Phone: 412-422-3463x4023
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