What is a route server?
A route server at an IXP enables multilateral peering through a single BGP session. We explain how it works, why it stays out of the AS_PATH and how it filters routes.
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A route server is a service running at an internet exchange point (IXP) that lets connected networks exchange BGP routes through one shared point instead of building a separate session with every partner. A participant sets up a single BGP session to the route server, advertises its prefixes and in return receives the prefixes of all other networks that also use the service. The route server is what makes multilateral peering possible, and it is one of the main reasons presence at an IXP delivers broad reach with minimal configuration effort.
Multilateral versus bilateral peering
Without a route server, operators build bilateral peering, a separate BGP session with each partner individually. With dozens of networks at an IXP that means dozens of sessions to configure and maintain. A route server replaces this with multilateral peering: a single session gives instant connectivity to every member of the fabric that is connected to the route server. Bilateral sessions still make sense for the most important partners, where full, individual policy control is needed, but for most connectivity multilateral is far more efficient.
Why a route server does not appear in the AS_PATH
A route server, per RFC 7947, is transparent to BGP. It mediates the exchange of routes but does not add its own ASN to the AS_PATH attribute, nor does it change the NEXT_HOP. As a result, traffic flows directly between the participants' networks rather than through the route server itself. From a routing point of view it looks as if the networks were peering directly. THINX runs its route servers under AS24748, but that number does not appear in the paths members see.
Route filtering and security
A modern route server does not relay routes blindly but filters them to protect the fabric from incorrect or malicious advertisements. Several layers of validation are used here:
- RPKI validation: dropping routes with an invalid origin based on signed ROAs.
- IRR filtering: building prefix allow-lists from route and as-set objects in the internet routing registries.
- Maximum prefix length and max-prefix limits that guard against route leaks.
- Alignment with MANRS, which standardises filtering and routing security at IXPs.
Route servers and AS202520 SkyPass
AS202520 SkyPass uses route servers at Polish internet exchanges to provide broad multilateral connectivity, and maintains additional bilateral peering with its most important partners. Networks that want to peer with us through a route server gain connectivity almost immediately, and we validate routes with RPKI and MANRS best practices. For operators without their own port at the IXP we offer remote access, letting them use multilateral peering without a physical presence in the data center.
Frequently asked questions
Does a route server appear in the AS_PATH?
No. A route server is transparent (RFC 7947) and does not add its ASN to the AS_PATH or change the NEXT_HOP, so traffic flows directly between the participants' networks.
How is a route server different from a route reflector?
A route server mediates peering between different networks (eBGP) at an IXP, while a route reflector scales iBGP inside a single autonomous system. They are two different tools.
Do I have to use a route server to peer at an IXP?
No, but it is the most convenient way. A single session to the route server gives connectivity to many networks at once. With key partners you can also set up bilateral peering.
Does a route server filter routes?
Yes, modern route servers validate route origin with RPKI, filter prefixes from IRR objects and apply limits, in line with MANRS practices.