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Where do ISPs normally put route reflectors for there MPLS networks

carl_townshend
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Hi All

Quick question, when we look at a typical ISP network that provides an MPLS network such as BT.

If they use route refectors, where would they normally put them ? what is the best place in a large network?

Also, if you run a BGP free core, such as I believe BT do for there MPLS, would you still need RR's ?

Cheers

1 Accepted Solution

Accepted Solutions

RR can be standalone.

for traffic Path through RR the answer is NO.
RR will reflect the VPNv4 from one PE to other, 
for example we have two PE 
PE1 and PE2, PE1 know the prefix for costumer connect to PE1 and need to send traffic toward it.
PE2 will use next-hop as PE1 loopback.
PE2 use IGP to decide the path "except the case of MPLS TE"
PE2 now add MPLS label and send traffic. 

this traffic not need to pass through RR it depend on IGP inside ISP Core.

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11 Replies 11

balaji.bandi
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Its all depends on what they provide ? if they provide only default route, you do not need any RR here.

 

how big your network ? Do you have own AS number and have multple providers you connect ?

 

BB

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Hi Balaj

They provide MPLS services to us and we have our own VRF on their network,  it is a general question about how would an ISP do it typically? what is they provide all routes and not just default?

if this just MPLS (no Internet), they do not offer anything, just hand over MPLS to you, you need to manage your own routing stuff.

 

If this is MPLS and Internet (then depends what contract)  - If you have Many ISP Link and own AS and IP address space, then you can ask full routing table to Manange Multi path ISP Traffic Engineering, if you have only ISP BT, then that only exist point you have in your network.

 

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Hello,

 

not really sure what you are after, but most large ISPs use multi-level route reflector topologies. in combination with reliance rules.

 

If you have some spare time, read the paper below:

 

https://www.researchgate.net/publication/220213166_BGP_route_prediction_within_ISPs

OK, 
MPLS core SP have many PE, 
if we want to connect many PE to other to form MP-BGP "iBGP" this need full mesh ....
meaning all PE must iBGP to all PE. that hard to design and admin so simply we add RR and connect all PE to this RR and from there we config PE as RR-clinet and hence no need full mesh between PE any more.

This is what I was after.

Do most ISP use BGP free core these days and use MPLS so no need for BGP on the P routers etc ?

since ISP core is BGP free so Yes all P router not config any BGP, it have IGP and MPLS only. 

Hi Guys

When ISP's have route reflectors in there networks that the PEs get their routes from, does any of the actual forwarding path for traffic go via the route reflector? or is that normally sent via other path?

Also would the route reflector be a standalone router or would it be on a core P router (when using mpls etc)

cheers

Hi @carl_townshend ,

 

does any of the actual forwarding path for traffic go via the route reflector? or is that normally sent via other path?

 

In the case of RR for services such as L3VPN, they are generally out of the forwarding path. 

 

Also would the route reflector be a standalone router or would it be on a core P router (when using mpls etc)

 

They are normally standalone devices and they could be physical or even virtual (such as XRv9k).

 

Regards,

Harold Ritter
Sr Technical Leader
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Provider network comfigured as per the Traffic Engineering based on the SP design, this may differ case to case.

 

How they design based on size of network and redundacy they offer.

 

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RR can be standalone.

for traffic Path through RR the answer is NO.
RR will reflect the VPNv4 from one PE to other, 
for example we have two PE 
PE1 and PE2, PE1 know the prefix for costumer connect to PE1 and need to send traffic toward it.
PE2 will use next-hop as PE1 loopback.
PE2 use IGP to decide the path "except the case of MPLS TE"
PE2 now add MPLS label and send traffic. 

this traffic not need to pass through RR it depend on IGP inside ISP Core.

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