Does anybody know why an IXP needs to have an ASN? Will that ASN appear in the AS-PATHs or will it be transparent?

  • 1
    Do you mean the IXP itself or the peers?
    – Zac67
    Commented Sep 16, 2019 at 7:54

1 Answer 1


In its most basic form, an IXP is nothing more than a large switch, allowing many networks to exchange traffic without having to interconnect with every other network on the IXP, thus reducing costs of cabling and route rports. As it only provides layer 1 and 2 connectivity, the IXP does not require to have an ASN.

However, IXPs often do a bit more: they host a website, customer portal, mail and possibly other services. Since they often do not wish to depend on hosting by one of the connected networks, they can get an ASN to host those services in.

Many IXPs also provide some routing services. Some IXPs offer a route collector, which is basically a BGP speaker which only receives routes but does not advertise any, to collect statistics about the IXPs. To setup BGP sessions with all IXP members a ASN is needed, and private ASNs are not really useful due to the chance of duplicates.

Also, many IXPs offer a route reflector service. This service allows IXP members to setup a BGP session with a router managed by the IXP to exchange routes with other other connected IXP members. Of course, this route reflector requires a ASN as well. The route reflector is only used to exchange routes (and next-hops on the peering platform), it's not in the forwarding path (else you would need routers and conncetions capable of handling a large part of the entire IXP platform). As the route reflector advertises routes with next-hops set to other peers, you will not see it in the forwarding path.

  • Thank you for your response. So, in order, a peer to configure his edge router's connection with the route reflector, should add a rule like: "Advertise ALL to <Route reflector's interface> <IXP ASN>? Afterward, does the AS_PATH of an advertisement that is received by another peer contain the ASN of the IXP, or it will be transparent, thus the next_hop will be the interface of the edge router that announced the route to the route reflector? Thank you again. Commented Sep 16, 2019 at 10:30
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    As I said, the route reflector is not in the forwarding path, it announces routes it receives with a next hop of the peer it receives the route from. If the reflector would be in the AS path, it would need to be able to forward all that traffic, which would require huge connections and routers on most IXPs.
    – Teun Vink
    Commented Sep 16, 2019 at 11:00
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    It also needs an ASN to originate the peering network itself.
    – abligh
    Commented Sep 16, 2019 at 21:22
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    You're right, @abligh, but only if you want those IPs to be publicly routable. Which is nice for ping replies, but may lead to other problems, like more specifics being announced dragging down entire exchanges.
    – Teun Vink
    Commented Sep 16, 2019 at 21:24
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    @konstantinosAR - You don't want to "Advertise ALL" - you only want to advertise your own address range eg: no defaults, no routes learnt from your transit provider or other peers. Hopefully your IXP filters all this, but it's good to do yourself just to be sure. Commented Sep 17, 2019 at 4:19

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