How many routed hops would be considered too many to leave an AS

Kind of a newbie questions, but I would like to know what the consensus is.


Thomas Gainer

Hmm, until it breaks the application?

Latency is what matters.

That is unless your TTL expires prematurely; in this case
defined as before the applications endpoints can reach each
other (which in turn could theoretically be a function of
latency as well).

I think that we can safely say that the answer is 255.

- Daniel Golding

Douglas Adams, had he done routing, would say 42. Sadly he's
  no longer with us.

  You won't get a concensus or a summary, but if I post
  you're sure to get many opinions with people correcting
  or disagreeing, or ranting about nonsequiter things
  in a pedantic way, so I'll try to help, or at least incite
  a flurry of vindicative responses.

  I believe the answer is A/ It Depends, and B/ Usually 6 to 8
  routed hops for each AS.

  In general, a network operator must be considerate of the
  lowest-common-denominator traffic on one's network.

  With regards to hop-count, many would say that Windows 95 (98?)
  is the LCD, as it emits IP packets (by default) with a TTL
  of 32 (Thirty-Two). I believe Win2k (maybe 98) has a default
  TTL of 128. I assume that WinME and WinXP are at 128 or more
  as well.

  It is fairly reasonable to consider that most (90+%) traffic
  goes through at most 4 ASes:

  (no AS) Client ->
  AS 1. Upstream AS of "client"
  AS 2. "Tier 1" Upstream to #1
  AS 3. "Tier 1" Peer and Upstream to #4
  AS 4. Upstream AS of "server"
  -> Server (no AS)

  Since there are 4 ASes, and 32 hops, each AS should get
  something close to 8 hops. Add a few at each end for
  aggregation, and you can get give each AS 6 hops, with
  some leftover for end-network traffic.


  or, MIN_HOPS_PER_AS = ( ( 32 - (2 * 2)) / 4 )
      MIN_HOPS_PER_AS = ( ( 32 - 4) / 4 )
      MIN_HOPS_PER_AS = ( 28 / 4 )
      MIN_HOPS_PER_AS = 7

  It is interesting to note that more IP elements, without more meshing,
  will create more hops. For example, a SONET network without significant
  meshing will have more IP hops than a fully meshed IP/ATM network. There
  are many many things of more significant importance than how many IP/L3
  hops a network has, however. Certain ATM and MPLS networks create
  logical meshes which decrease (IP L3) hop counts in certain
  circumstances. Pros/Cons all the way around.


Thus spake Thomas Gainer (
on or about Mon, May 14, 2001 at 05:59:35PM -0400: