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Why do IXPs need ASN?

Internet exchange pointHow do Autonomous Systems work?Order of entries in “show ip bgp x.x.x.x”16 and 32-bit ASN compatibility of BGP routersHow to tell if an ASN belongs to a hosting company/ISP or a “regular” organizationWhy does source RTBH need uRPFWhy do we need MPLS when implementing L2/L3 VPNs?Use case for two BGP ASNs?Reasons for buying ASN for organisation that are located at single place

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5

1

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

bgp

share|improve this question

edited Sep 16 at 14:31

Machavity

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asked Sep 16 at 4:33

konstantinosARkonstantinosAR

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• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Do you mean the IXP itself or the peers?
  
  – Zac67
  Sep 16 at 7:54
  

  
  
  
  

add a comment
 | 

5

1

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

bgp

share|improve this question

edited Sep 16 at 14:31

Machavity

9988 bronze badges

asked Sep 16 at 4:33

konstantinosARkonstantinosAR

12744 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Do you mean the IXP itself or the peers?
  
  – Zac67
  Sep 16 at 7:54
  

  
  
  
  

add a comment
 | 

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

bgp

share|improve this question

edited Sep 16 at 14:31

Machavity

9988 bronze badges

asked Sep 16 at 4:33

konstantinosARkonstantinosAR

12744 bronze badges

share|improve this question

edited Sep 16 at 14:31

Machavity

9988 bronze badges

asked Sep 16 at 4:33

konstantinosARkonstantinosAR

12744 bronze badges

share|improve this question

edited Sep 16 at 14:31

Machavity

9988 bronze badges

asked Sep 16 at 4:33

konstantinosARkonstantinosAR

12744 bronze badges

edited Sep 16 at 14:31

Machavity

9988 bronze badges

edited Sep 16 at 14:31

Machavity

9988 bronze badges

asked Sep 16 at 4:33

konstantinosARkonstantinosAR

12744 bronze badges

asked Sep 16 at 4:33

konstantinosARkonstantinosAR

12744 bronze badges

1 Answer
1

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11

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.

share|improve this answer

answered Sep 16 at 8:47

Teun Vink♦Teun Vink

13.2k55 gold badges3535 silver badges5858 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  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.
  
  – konstantinosAR
  Sep 16 at 10:30
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  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♦
  Sep 16 at 11:00
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  It also needs an ASN to originate the peering network itself.
  
  – abligh
  Sep 16 at 21:22
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  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♦
  Sep 16 at 21:24
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @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.
  
  – Benjamin Dale
  Sep 17 at 4:19
  
  

  
  
  
  

 | 
show 2 more comments

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11

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.

share|improve this answer

answered Sep 16 at 8:47

Teun Vink♦Teun Vink

13.2k55 gold badges3535 silver badges5858 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  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.
  
  – konstantinosAR
  Sep 16 at 10:30
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  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♦
  Sep 16 at 11:00
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  It also needs an ASN to originate the peering network itself.
  
  – abligh
  Sep 16 at 21:22
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  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♦
  Sep 16 at 21:24
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @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.
  
  – Benjamin Dale
  Sep 17 at 4:19
  
  

  
  
  
  

 | 
show 2 more comments

11

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.

share|improve this answer

answered Sep 16 at 8:47

Teun Vink♦Teun Vink

13.2k55 gold badges3535 silver badges5858 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  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.
  
  – konstantinosAR
  Sep 16 at 10:30
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  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♦
  Sep 16 at 11:00
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  It also needs an ASN to originate the peering network itself.
  
  – abligh
  Sep 16 at 21:22
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  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♦
  Sep 16 at 21:24
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @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.
  
  – Benjamin Dale
  Sep 17 at 4:19
  
  

  
  
  
  

 | 
show 2 more comments

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.

share|improve this answer

answered Sep 16 at 8:47

Teun Vink♦Teun Vink

13.2k55 gold badges3535 silver badges5858 bronze badges

share|improve this answer

answered Sep 16 at 8:47

Teun Vink♦Teun Vink

13.2k55 gold badges3535 silver badges5858 bronze badges

answered Sep 16 at 8:47

Teun Vink♦Teun Vink

13.2k55 gold badges3535 silver badges5858 bronze badges

answered Sep 16 at 8:47

Teun Vink♦Teun Vink

13.2k55 gold badges3535 silver badges5858 bronze badges