1. Backbone addresses: ISPs that hide interface addresses and/or primary loopback addresses, and best practices for doing so? (e.g. traceroutes don't break, but the router uses say Loopback1 address to respond to them, while iBGP uses Loopback0. All Loopback0 address blocks can be filtered at borders.)

since ibgp's should be peered w/ loopbacks, loopback protection is all needed as as far as this bgp hysteria goes. so loopback0 with "secret" addresses for ibgp peering, use a loopback1 to publish router ip addrs to public via looking glass, etc. next thing to protect is customer ebgp sessions. some providers don't even route the p2p /30 links used between cust and their backbone (i.e. Sprint). so that's up to you. some backbones even filter all traffic destined to backbone prefixes at ingress points (border routers, cust edge routers)... for example.. att being one. for example, here comes random test: starbucks blahdy $ traceroute -M 8 12.123.205.65 traceroute to 12.123.205.65 (12.123.205.65), 64 hops max, 44 byte packets 8 jfk-brdr-02.inet.qwest.net (205.171.230.21) 6.404 ms 6.138 ms 6.145 ms 9 * qwest-gw.n54ny.ip.att.net (192.205.32.169) 6.465 ms !X * all above options don't necessarily break traceroute as long as you implement it with care... -J

2. Public IX addresses: ISPs that do not redistribute the IX prefix into their iBGP or IGP and do not use external next-hops (except local to the connected border router), but instead use the loopback of the border router when propogating these routes within their iBGP mesh. This should not break traceroutes "through" the exchange, but will break any traffic such as ping, spoofed packets, etc. to the exchange from a non-connected router.

Can anyone provide pro/con, better description of config templates for doing this, and/or discussion of major networks that choose to do this, or not do this?

Cheers, -Lane

-- James Jun TowardEX Technologies, Inc. Technical Lead Network Design, Consulting, IT Outsourcing james@towardex.com Boston-based Colocation & Bandwidth Services cell: 1(978)-394-2867 web: http://www.towardex.com , noc: www.twdx.net

On Apr 22, 2004, at 6:36 PM, Lane Patterson wrote:

Although someone mentioned using non-routable /30 or /31's on private eBGP peers, there hasn't been much broad-ranging discussion of keeping internal infrastructure addresses non-routable. I am thinking of a couple different things here:

1. Backbone addresses: ISPs that hide interface addresses and/or primary loopback addresses, and best practices for doing so? (e.g. traceroutes don't break, but the router uses say Loopback1 address to respond to them, while iBGP uses Loopback0. All Loopback0 address blocks can be filtered at borders.)

If you use multi-hop peering with loopback0, why bother changing the traceroute replies? Alternatively, if you make all traceroute replies from loopback1, then why bother turning on multi-hop BGP? Hrmmm, would the GTSM work with loopback peering? ISTR it allowed a TTL of 254, which should make it to the loopback interface.

2. Public IX addresses: ISPs that do not redistribute the IX prefix into their iBGP or IGP and do not use external next-hops (except local to the connected border router), but instead use the loopback of the border router when propogating these routes within their iBGP mesh. This should not break traceroutes "through" the exchange, but will break any traffic such as ping, spoofed packets, etc. to the exchange from a non-connected router.

Excellent idea. And one which is, I believe, being used by several people already. Perhaps more wide spread use would help? I like the second one more than the first since the first is more of a security-through-obscurity than anything else. But even obscurity is better security than nothing. OTOH, the best security measure right now would be to do something like OpenBSD's random ephemeral port algorithm into the router OSes. Then this "vulnerability" would be far, far less vulnerable. -- TTFN, patrick