RE: Pitfalls of annoucing /24s
What about the /24's that many ISPs (especially tier 2-3) are assigning to multi-homed customers? What about an IX or "critical infrastructure providers" that may be issued a /24 from ARIN (Policy 2001-3)? Although it may be rare that a large aggregate would become unreachable to a "large" network, doesn't the possibility exist that a customer with a /24 would become unreachable (to some) due to the aggregate dropping out even though the /24 should still be reachable? That scenario may not be very likely, but the question of assymetric routing and one's ability to balance traffic become issues. Assigning a lower preference to /24's would be a lot friendlier than just throwing them away. If I am way off base, I fully expect to be corrected (with volume). My flame retardant suit is in place. Michael -----Original Message----- From: owner-nanog@merit.edu [mailto:owner-nanog@merit.edu] On Behalf Of Phil Rosenthal Sent: Wednesday, October 15, 2003 4:47 PM To: John Palmer Cc: nanog@merit.edu Subject: Re: Pitfalls of annoucing /24s http://info.us.bb.verio.net/routing.html#PeerFilter That's how Verio does it, and I assume, that's how most people who filter by length do it as well. --Phil On Oct 15, 2003, at 4:40 PM, John Palmer wrote:
Good question.
You know there are thousands of legacy /24's out there that were allocated by IANA as /24's How can you aggregate them up if all you have is the
/24?
To those who filter out /24's - how is this done - just by the netmask
size?
----- Original Message ----- From: "Jean-Christophe Smith" <jsmith@vitalstream.com> To: <nanog@merit.edu> Sent: Wednesday, October 15, 2003 15:34 Subject: Pitfalls of annoucing /24s
In current practice would there be serious jeopardy of portions of
the
internet not being able to reach this address space due to bgp filters or other restrictions? What is the smallest acceptable block of IPs that
can be announced without adverse or unpredictable results? Verio would most likely be picking up these routes from us. I don't want to cause a religious debate, but I am interested in what the industry consensus is.
I'm just doing some research, any comments would be appreciated.
Thanks, Jean-Christophe Smith
--Phil Rosenthal ISPrime, Inc.
On Oct 15, 2003, at 5:24 PM, H. Michael Smith, Jr. wrote:
What about the /24's that many ISPs (especially tier 2-3) are assigning to multi-homed customers? What about an IX or "critical infrastructure providers" that may be issued a /24 from ARIN (Policy 2001-3)?
As long as it's provider assigned, and your provider announces the supernet that the /24 is from, it will still work. If you announce PI space out of the old class A space in /24's, many networks wont be able to reach you.
I have a /24 allocated to my by XO Communications in Phoenix, AZ (67.X.X.0/24). I am currently announcing it to Verio in Europe. A friend of mine that is an XO customer in Phoenix with BGP to XO can get to that address block within XO's network. But on the flip side. I also have a /22 from AT&T (12.X.X.0/22). When I announce that network block to Verio in Europe (and nowhere else), only certain places get to the Europe location. Networks that prefer AT&T go to AT&T's network and die since the route isn't there. I don't know if I am missing something but it think it may have to do with how the network's peering/filter schemes work. I may just be walking around the problem since I am a transit customer of Verio and they normally filter. -Andy --- Phil Rosenthal <pr@isprime.com> wrote:
On Oct 15, 2003, at 5:24 PM, H. Michael Smith, Jr. wrote:
What about the /24's that many ISPs (especially tier 2-3) are
assigning
to multi-homed customers? What about an IX or "critical infrastructure providers" that may be issued a /24 from ARIN (Policy 2001-3)?
As long as it's provider assigned, and your provider announces the supernet that the /24 is from, it will still work. If you announce PI space out of the old class A space in /24's, many networks wont be able to reach you.
Hi Andy, Verio says they accept old class-a space at the /22 orshorter level so that isn't it. I am fairly certain you can not successfully multihome with PA class-A space.. If you are not announcing that /22 to AT&T then anyone that is single-homed to AT&T (or preferring them) will probably not be able to reach your /22. I ran into this problem with some 4/8 space that Level3 assigned to me by mistake. So you are dealing with more of a Policy issue rather than general prefix filter. -Scott ----- Original Message ----- From: "Andy Ellifson" <andy@ellifson.com> To: <nanog@merit.edu> Sent: Wednesday, October 15, 2003 6:28 PM Subject: Re: Pitfalls of annoucing /24s
I have a /24 allocated to my by XO Communications in Phoenix, AZ (67.X.X.0/24). I am currently announcing it to Verio in Europe. A friend of mine that is an XO customer in Phoenix with BGP to XO can get to that address block within XO's network.
But on the flip side. I also have a /22 from AT&T (12.X.X.0/22). When I announce that network block to Verio in Europe (and nowhere else), only certain places get to the Europe location. Networks that prefer AT&T go to AT&T's network and die since the route isn't there. I don't know if I am missing something but it think it may have to do with how the network's peering/filter schemes work.
I may just be walking around the problem since I am a transit customer of Verio and they normally filter.
-Andy
--- Phil Rosenthal <pr@isprime.com> wrote:
On Oct 15, 2003, at 5:24 PM, H. Michael Smith, Jr. wrote:
What about the /24's that many ISPs (especially tier 2-3) are
assigning
to multi-homed customers? What about an IX or "critical infrastructure providers" that may be issued a /24 from ARIN (Policy 2001-3)?
As long as it's provider assigned, and your provider announces the supernet that the /24 is from, it will still work. If you announce PI space out of the old class A space in /24's, many networks wont be able to reach you.
participants (4)
-
Andy Ellifson -
H. Michael Smith, Jr. -
K. Scott Bethke -
Phil Rosenthal