[ixpmanager] Techniques to influence inbound (download) traffic across multiple IXPs with /24 prefixes

[Douglas Fischer]

If there were two networks that met not through IXPs, but through their own
links... How would this be resolved?

MED - Multi Exit Discriminator

For this to work over IXPs, 3 requirements need to be met.

A) Transparent MED. Route-Servers need to forward the received MED.

B) From the point of view of the participants sending routes to the
Route-Servers:
B.1) Stop the WRONG methodology of forcing more specific routes to be
advertised to Route-Servers, as well as excessive prepends.
B.2) Apply MEDs that reflect the preference for each path.
Note: I really like the scenario where the MED is used as Cumulative
IGP-Cost, and the IGP cost reflects distance in kilometers, or latency in
microseconds.

C) From the perspective of participants receiving routes from Route-Servers:
B.1) Stop the WRONG methodology of indiscriminately increasing local-pref
for all routes received from Route-Servers.
B.2) Start comparing and analyzing the MED for eBGP, especially in IXPs,
activating parameters such as "always-compare-med",
"compare-different-as-med", and "deterministic-med".

Part "A", from the route-servers... is easy!
Parts "B" and "C", which depend on network operators ceasing to look at
their own navels, are more difficult.
I only end up seeing this level of maturity in large carriers.

Em qua., 7 de jan. de 2026 às 13:44, Salvador Bertenbreiter via ixpmanager <
ixpmanager at inex.ie> escreveu:

> Hi everyone,
>
> Hope you’re doing well. I’d like to ask how you approach inbound traffic
> engineering (download traffic) when you’re connected to multiple IXPs (some
> local, some remote) and you only have small prefixes (e.g., /24), so
> announcing more/less specifics isn’t really an option.
>
> In that scenario, what methods have worked for you besides simple AS-path
> prepending (e.g., no prepend on local IX, prepend 1 on the closest remote
> IXP, prepend 2 on the next, etc.)?
>
> Thanks in advance for any guidance or real-world examples.
>
> --
> Salvador
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-- 
Douglas Fernando Fischer
Engº de Controle e Automação
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