I was talking to a set of customers of ours today, some of whom were dealing with some long prefixes which were being heard originating within SprintLink and propagating to MCI. This caused me to audit how well our edge filtering was working, and to spend some time reworking the filters that match long prefixes. I shall post the text of the filter here tomorrowishly so that everyone can look at how gross it is, comments-and-all. Meanwhile, however, it seems correctly to implement this policy, which is now many months old: reject BGP announcements which: -- are an old-style classful A network with a mask longer than 8 bits except for exp39, 39.0.0.0/8, where we allow prefixes to be up to 24 bits long and the two operational IBM prefixes: 9.20.0.0/18 and 9.2.0.0/16. -- are an old-style classful B network with a mask longer than 16 bits -- are in the range of 206.0.0.0/8 to 239.0.0.0/8 with a mask longer than 18 bits -- has a mask longer than 24 bits [RSN we will also reject RFC1597 prefixes in this list; currently another mechanism is used to avoid hearing RFC1597 prefixes.] Note that we accept prefixes in the range of 192.0.0.0/8 - 205.0.0.0/8 (known cordially as The Swamp) as long as the prefix is at least 24 bits long. Also, this is not cast in concrete; there was some discussion of possibly allowing /19s at some point, and also some discussion about attacking the top several octets of The Swamp, by allowing only /23s or shorter. There has also been some talk about relaxing the maximum mask length on 1.0.0.0/8 - 126.0.0.0/8 to something a bit longer. I suspect all of this will be revisited at intervals, however, I believe that the consensus at the NANOG in Pittsburgh was that it'd be a good idea to post things like this here. Also, I note that we currently are not applying this list *outbound* or against customer BGP sessions. The reason for this is quite simple -- call it a (very) small incentive for other folks we peer with to apply the same kind of inbound filter against very long prefixes. I will admit that this is more a case of oversight than direct engineering terrorism, however, at some point we certainly will begin stopping the announcement of this type of long prefix to our external peers, and in the mean time it's useful to know that there really are people out there who notice /32s and the like floating around, and who complain about them. That's a good thing. Personally, I'd be grateful if people *did* toss long prefixes gotten from SprintLink (and elsewhere), so long as they tell people about it. Penultimately, this filter is currently deployed at all of SprintLink's edges, but not within ICM AS 1800. This is principally to allow for differential comparisons between what long prefixes the two networks see over the next short while. That makes it easier to see what we're filtering out on the SprintLink side, in hopes of catching botches and spending a couple of days firing off email to people responsible for announcing long prefixes, explaining why they should stop. Finally, the list of the prefixes affected by the filter, obtained by differential comparison between SL and ICM, is below. The classful subnets were noted in CIDRD; the stuff in 206/8 is of some interest to the very-newly-connected (connected, in fact, by people who probably didn't warn their customers of the very very very old announcements I made here and on CIDRD about precisely this filtering on 206/8, on 13 April, 23 June, 24 August, and other dates, and at NANOGs and IETFs galore) are interesting: many (more than 120) are covered by idempotent less-specific aggregates anyway, and others seem to be easily aggregatable, or just don't seem to go anywhere yet. Sean. - -- Sean Doran <smd@sprint.net> - -- cut here ---- [subnets of classful A space, classful B space, and all >/24s] [ prefix as-path ] 129.40.43.0/24 690 2685 129.40.202.0/24 690 2685 129.159.147.0/24 1755 2874 129.159.148.0/24 1755 2874 131.115.186.0/24 1755 3300 131.115.187.0/24 1755 3300 131.115.188.0/24 1755 3300 131.116.136.0/26 1755 3300 131.116.136.64/26 1755 3300 131.116.136.128/26 1755 3300 131.116.153.64/26 1755 3300 132.174.100.0/24 690 1325 4373 139.92.1.0/24 1804 1128 1275 145.17.100.0/24 1801 786 1849 147.186.219.64/26 1755 2874 148.185.45.0/24 1801 786 1849 148.252.1.0/24 1801 786 1849 149.212.64.0/23 1755 1759 544 151.185.100.0/22 3561 151.185.104.0/22 3561 151.185.108.0/23 3561 151.185.110.0/24 3561 152.129.186.0/24 3561 4478 155.140.123.0/24 1801 786 1849 159.24.7.64/26 3561 4286 159.189.128.0/19 3561 279 2048 {33035} 160.8.106.0/24 1755 2874 160.8.110.0/23 1755 2874 161.52.192.0/19 1653 2843 2845 164.9.190.0/31 1755 3300 164.9.194.0/31 1755 3300 164.9.196.0/24 1755 3300 166.38.40.0/24 3561 166.147.0.0/18 3561 166.147.192.0/18 3561 166.150.0.0/18 3561 166.150.64.0/18 3561 166.150.128.0/18 3561 166.150.192.0/18 3561 166.151.0.0/18 3561 166.151.64.0/18 3561 166.151.128.0/18 3561 166.151.192.0/18 3561 167.170.7.0/24 1755 3300 3302 3313 170.194.51.0/24 1801 786 1849 171.25.128.0/20 1755 3300 171.25.144.0/21 1755 3300 192.108.149.128/26 1804 1128 2605 1902 1922 193.172.1.192/27 1804 1128 2043 194.45.40.161/32 1755 517 194.45.120.0/26 1755 517 194.45.120.64/26 1755 517 194.45.120.128/26 1755 517 194.45.121.0/28 1755 517 194.45.121.128/28 1755 517 194.45.121.192/28 1755 517 194.45.236.64/28 1755 517 194.45.236.80/28 1755 517 198.226.1.80/28 3561 - -- [206/8 more-specifics] [ prefix as-path ] 206.12.1.0 3561 577 271 206.12.2.0 3561 577 271 206.12.8.0 3561 577 271 206.12.10.0 3561 577 271 206.12.11.0 3561 577 271 206.12.15.0 3561 577 271 206.12.16.0 3561 577 271 206.12.17.0 3561 577 271 206.12.18.0 3561 577 271 206.12.19.0 3561 577 271 206.12.20.0 3561 577 271 206.12.21.0 3561 577 271 206.12.22.0 3561 577 271 206.12.23.0 3561 577 271 206.12.24.0 3561 577 271 206.12.25.0 3561 577 271 206.12.26.0 3561 577 271 206.12.32.0 3561 577 271 206.12.33.0 3561 577 271 206.12.34.0 3561 577 271 206.12.35.0 3561 577 271 206.12.36.0 3561 577 271 206.12.37.0 3561 577 271 206.12.38.0 3561 577 271 206.12.39.0 3561 577 271 206.12.40.0 3561 577 271 206.12.41.0 3561 577 271 206.12.42.0 3561 577 271 206.12.43.0 3561 577 271 206.12.44.0 3561 577 271 206.12.45.0 3561 577 271 206.12.46.0 3561 577 271 206.12.47.0 3561 577 271 206.12.59.0 3561 577 271 206.12.96.0 690 1331 1691 206.12.101.0 3830 4064 3609 206.12.108.0 3830 4064 3609 206.12.111.0 690 1331 1691 206.12.112.0 3830 4064 3609 206.12.113.0 3830 4064 3609 206.12.114.0 3830 4064 3609 206.12.115.0 3830 4064 3609 206.12.117.0 690 1331 1691 206.12.118.0 3830 4064 3609 206.12.119.0 3830 4064 3609 206.12.126.0 3830 4064 3609 206.12.134.0 690 1331 1691 206.12.151.0 690 1331 1691 206.12.153.0 3830 4064 3609 206.12.154.0 3561 2493 206.12.156.0 3830 4064 3609 206.12.158.0 3830 4064 3609 206.12.159.0 3830 4064 3609 206.12.168.0 3830 4064 3609 206.12.169.0 3830 4064 3609 206.12.170.0 3830 4064 3609 206.12.171.0 3830 4064 3609 206.12.172.0 3830 4064 3609 206.12.173.0 3830 4064 3609 206.12.174.0 3830 4064 3609 206.12.175.0 690 1331 1691 206.12.176.0 690 1331 1691 206.12.177.0 690 1331 1691 206.12.178.0 690 1331 1691 206.12.179.0 690 1331 1691 206.12.180.0 690 1331 1691 206.12.181.0 690 1331 1691 206.12.186.0 3830 4064 3609 206.12.187.0 3561 2493 206.12.188.0 690 1331 1691 206.12.202.0/23 3561 5071 206.12.206.0 3561 5071 206.12.208.0 3561 5071 206.12.226.0 690 1331 1691 206.12.227.0 690 1331 1691 206.12.229.0 690 1331 1691 206.12.230.0 690 1331 1691 206.12.237.0 3561 5071 206.12.238.0/23 3561 5071 206.12.241.0 690 1331 1691 206.12.247.0 690 1331 1691 206.13.0.0/19 3830 4200 5671 206.13.32.0/19 3830 4200 5672 206.13.64.0/19 3830 4200 5672 206.13.96.0/20 3830 4200 5672 206.15.32.0/19 3561 1746 206.15.64.0/19 3830 4200 4540 206.15.96.0/19 3561 560 206.15.128.0/19 3561 560 206.16.206.0 1740 206.16.208.0 1740 206.16.209.0 1740 206.16.210.0 1740 206.16.211.0 1740 206.16.212.0 1740 206.16.213.0 1740 206.16.214.0 1740 206.16.215.0 1740 206.16.219.0 1740 206.16.221.0 1740 206.16.222.0 1740 206.17.4.0 1740 206.17.18.0 1740 206.24.0.0/19 3561 206.24.8.0/23 3561 206.24.28.0/23 3561 206.24.32.0/19 3561 206.24.44.0 3561 206.24.64.0/19 3561 206.24.96.0/19 3561 206.24.128.0/21 3561 206.24.136.0/21 3561 206.24.152.0/21 3561 206.24.160.0/21 3561 206.24.168.0/21 3561 206.24.172.0/22 3561 206.24.176.0/21 3561 206.24.192.0/21 3561 206.24.200.0/21 3561 206.24.216.0/21 3561 206.24.224.0/21 3561 206.25.0.0/19 3561 206.25.32.0/19 3561 206.25.36.0/23 3561 206.25.64.0/20 3561 206.25.64.0/19 3561 206.25.86.0/23 3561 206.25.88.0/22 3561 206.25.92.0/23 3561 206.25.94.0 3561 206.25.96.0/19 3561 206.25.128.0/19 3561 206.25.160.0/19 3561 206.25.168.0/23 3561 206.25.182.0 3561 206.25.184.0/23 3561 206.25.192.0/19 3561 206.25.224.0/19 3561 206.25.226.0/23 3561 206.26.0.0/19 3561 206.26.10.0/23 3561 206.26.32.0/19 3561 206.26.50.0/23 3561 206.26.64.0/19 3561 206.26.96.0/23 3561 5650 206.26.96.0/19 3561 206.26.98.0/23 3561 206.26.128.0/19 3561 206.26.142.0/23 3561 206.26.160.0/19 3561 206.26.192.0/19 3561 206.26.224.0/19 3561 206.27.64.0/19 3561 206.27.96.0/19 3561 206.27.128.0/19 3561 206.27.138.0/23 3561 206.27.160.0/19 3561 4947 206.27.192.0/19 3561 206.27.206.0 3830 4991 4959 206.27.207.0 3830 4991 4959 206.27.224.0/19 3561 206.27.236.0/23 3561 206.28.0.0/19 3561 206.28.16.0/22 3561 206.28.32.0/19 3561 206.28.64.0/19 3561 206.28.96.0/19 3561 206.28.110.0/23 3561 206.28.120.0/23 3561 206.28.122.0/23 3561 206.28.128.0/19 3561 206.28.158.0 3561 206.28.160.0/19 3561 206.28.172.0/23 3561 206.28.192.0/19 3561 206.28.224.0/19 3561 206.29.0.0/23 3561 206.29.0.0/19 3561 206.29.8.0/23 3561 206.29.14.0/23 3561 206.29.24.0/23 3561 206.29.29.0 3561 206.29.32.0/23 3561 206.29.32.0/19 3561 206.29.34.0/23 3561 206.29.36.0/23 3561 206.29.39.0 3561 206.29.64.0/20 3561 206.29.64.0/19 3561 206.29.88.0/21 3561 206.29.96.0/19 3561 206.29.108.0 3561 206.29.108.0/23 3561 206.29.114.0/23 3561 206.29.128.0/19 3561 206.29.160.0/19 3561 206.29.192.0/19 3561 5650 206.29.224.0/19 3561 206.30.0.0/19 3561 206.30.32.0/21 3561 206.30.32.0/19 3561 206.30.64.0/19 3561 206.30.96.0/19 3561 206.30.128.0/20 3561 206.30.128.0/19 3561 206.30.160.0/19 3561 206.30.180.0/23 3561 206.30.192.0/19 3561 206.30.208.0/23 3561 206.30.224.0/19 3561 206.30.228.0/23 3561 206.31.0.0/19 3561 206.31.32.0/19 3561 206.31.64.0/19 3561 206.31.96.0/19 3561 206.31.110.0/23 3561 206.31.116.0/23 3561 206.31.128.0/19 3561 206.31.130.0/23 3561 206.31.160.0/19 3561 206.31.192.0/19 3561 206.31.224.0/19 3561 206.31.226.0/23 3561 206.37.1.0 568 206.37.2.0 568 206.37.13.0 568 206.40.32.0/19 3830 4200 3720 206.40.64.0/19 701 3967 206.40.160.0/20 3561 114 206.40.192.0 3830 3491 4565 206.40.192.0/19 3830 3491 4565 206.40.221.0 3830 3491 4565 206.41.0.0/19 3561 206.41.32.0/21 3561 5109 206.41.64.0/21 3830 4388 4920 206.41.96.0/21 3561 206.41.160.0/22 3830 4200 206.41.164.0 3830 4200 206.41.165.0 3830 4200 206.41.166.0 3830 4200 206.41.167.0 3830 4200 206.41.168.0/23 3830 4200 206.41.170.0 3830 4200 206.41.171.0 3830 4200 206.41.172.0 3830 4200 206.41.173.0 3830 4200 206.41.177.0 3830 4200 206.41.178.0 3830 4200 206.41.214.0/23 3561 206.41.216.0/21 3561 206.43.0.0/19 3830 4388 206.43.36.0/22 3830 4388 206.43.64.0/19 701 3838 3838 3838 3838 3838 3838 3838 206.43.96.0 3830 4388 206.43.98.0/23 3830 4388 206.43.100.0 3830 4388 206.43.104.0 3830 4388 206.43.104.0/21 3830 4388 206.43.105.0 3830 4388 206.43.106.0 3830 4388 206.43.111.0 3830 4388 206.43.112.0/20 3830 4388 206.43.176.0/21 3830 4388 206.43.182.0 3830 4388 206.43.224.0/22 3830 4388 206.53.64.0/22 3830 4200 206.53.128.0 3561 206.53.224.0/19 3561 206.54.160.0/19 3561 206.54.192.0/22 3561 2150 226 206.55.1.0 3561 6618 206.55.2.0 3561 6618 206.55.3.0 3561 6618 206.55.4.0 3561 6618 206.55.5.0 3561 6618 206.55.6.0 3561 6618 206.55.10.0 3561 6618 206.55.12.0 3561 6618 206.55.13.0 3561 6618 206.55.14.0 3561 6618 206.55.15.0 3561 6618 206.55.16.0 3561 6618 206.55.17.0 3561 6618 206.55.18.0 3561 6618 206.55.19.0 3561 6618 206.55.20.0 3561 6618 206.55.21.0 3561 6618 206.55.23.0 3561 6618 206.55.24.0 3561 6618 206.55.25.0 3561 6618 206.55.26.0 3561 6618 206.55.30.0 3561 6618 206.55.55.0 3561 6618 206.55.56.0 3561 6618 206.55.57.0 3561 6618 206.55.58.0 3561 6618 206.55.59.0 3561 6618 206.55.60.0 3561 6618 206.55.61.0 3561 6618 206.55.62.0 3561 6618 206.55.63.0 3561 6618 206.55.128.0/19 3561 2150 226 206.62.4.0/22 3830 4200 206.64.48.0 701 3791 206.64.49.0 701 3791 206.64.50.0 701 3791 206.64.52.0 701 3791 206.64.53.0 701 3791 206.64.58.0 701 3791 206.64.59.0 701 3791 206.64.60.0 701 3791 206.64.62.0 701 3791 206.64.63.0 701 3791 206.64.123.0 701 5706 206.64.128.0 701 3397 206.64.130.0 701 3397 206.64.131.0 701 3397 206.64.132.0 701 3397 206.64.134.0 701 3397 206.64.147.0 3561 114 206.64.159.0 3830 4992 3803 206.66.1.0 701 4278 206.66.2.0 701 4278 206.66.3.0 701 4278 206.66.176.0 701 4206 206.66.177.0 701 4206 206.66.192.0 701 4438 206.71.128.0/21 701 206.71.160.0/21 3561 206.71.224.0/19 3561 3674 206.72.128.0/19 701 206.72.224.0/22 3561 279 206.73.70.0 3561 2150 226 1220 206.73.71.0 3561 2150 226 1220 206.73.72.0/22 3561 2150 226 1220 206.73.76.0/23 3561 2150 226 1220 206.73.78.0 3561 2150 226 1220 206.75.4.0 3561 577 542 206.75.6.0 3561 577 542 206.75.7.0 3561 577 542 206.75.19.0 690 1331 1684 206.75.224.0 3561 577 542 206.75.225.0 3561 577 542 206.75.250.0 690 1331 1684 206.80.0.0/19 3830 4447 206.80.64.0 1740 206.80.65.0 1740 206.80.66.0 1740 206.80.67.0 1740 206.80.68.0 1740 206.80.69.0 1740 206.80.70.0 1740 206.80.71.0 1740 206.80.224.0/21 701 206.81.224.0/19 701 4232 206.96.0.0/19 3561 206.96.32.0/19 3561 206.96.64.0/19 3561 206.96.96.0/23 3561 206.96.96.0/19 3561 206.96.104.0/22 3561 206.96.128.0/19 3561 206.96.160.0/21 3561 206.96.160.0/19 3561 206.96.192.0/19 3561 206.96.224.0/19 3561 206.97.0.0/19 3561 206.97.32.0/19 3561 206.97.64.0/20 3561 206.97.64.0/19 3561 206.97.96.0/19 3561 206.97.128.0/19 3561 206.97.160.0/19 3561 206.97.192.0/19 3561 206.97.224.0/19 3561 206.98.0.0/19 3561 206.98.32.0/23 3561 206.98.32.0/19 3561 206.98.64.0/19 3561 206.98.96.0/19 3561 206.98.128.0/19 3561 206.98.160.0/19 3561 206.98.192.0/19 3561 206.98.224.0/19 3561 206.99.0.0/19 3561 206.99.32.0/19 3561 206.99.64.0/19 3561 206.99.90.0 3561 206.99.96.0/19 3561 206.99.128.0/19 3561 206.99.160.0/19 3561 206.99.192.0/19 3561 206.99.224.0/19 3561 206.100.0.0/19 3561 206.100.32.0/19 3561 206.112.32.0/19 701 5053 206.116.1.0 3561 2493 206.116.4.0 3561 2493 206.116.5.0 3561 2493 206.116.6.0 3561 2493 206.116.10.0 3561 2493 206.116.11.0 3561 2493 206.128.23.0 701 3791 206.139.72.0/23 3561 206.195.64.0/19 3561 3909 206.196.0.0/20 3561 206.196.32.0/20 3830 4991 206.196.64.0/20 3561 206.196.96.0/20 3561 4205 206.196.160.0/19 690 2548 206.197.2.0 701 206.197.19.0 3561 206.197.51.0 701 206.197.68.0 690 1332 206.197.95.0 3830 3491 3739 206.197.101.0 86 225 206.197.103.0 3830 4992 206.197.133.0 3830 4992 206.197.138.0 1740 206.197.143.0 3561 206.197.184.0 3830 4994 206.197.204.0 701 2927 206.201.192.0/20 701 206.209.176.0/21 3561 206.209.183.0 3561 206.209.184.0/22 3561 206.209.188.0/23 3561