MPLS-TE Design Question

[Marwan ALshawi]

Hi

from practical real networks design what is going to be the answer to below:

- When to use MPLS-TE signaling as RSVP vs LDP and why in each case

- When to use the TE between PEs and to use it between Ps in an SP network and each case what is the recommend signaling RSVP or LDP

e.g for VOIP to be placed in TE using DS-TE with CBTS is it better to have the TE between PEs, if yes when we need it between Ps )

- Can we have mix of TEs between PEs and between Ps ? when this is useful ?

- Auto FRR vs manual

Thanks

Marwan

[Mohamed Sobair]

Hello Marwan,

MPLS-TE cant be established over an LDP, it has to be RSVP Signaled path in order to establish an end to end TE LSP. Traffic Engineering uses Special OSPF Opaque LSAs and ISIS TLVs, and those are the only Protocols that can carry RSVP Signaling messages.

However, You can Tunnel LDP Over an RSVP TE Tunnel if its a requirement in one of the following Scenarios:

1- when your Core is configured with RSVP only between P routers and there is no LDP on the Core. LDP Tunnel over RSVP is needed.

2- If you want to provide a redundant LDP Session over an RSVP TE Tunnel.

For the Use of TE between Ps or PEs, SPs normally do it between PEs according to their Service Level Agreement with the Customers, to make sure some Customers traffic is always differenciated from normal traffic path.

For the use of TE between P routers, SPs do it to provide more faster convergence Core!

With TE - Fast Reroute, you ensure convergence with lesser than 50 milliseconds!

HTH

Mohamed

[Marwan ALshawi]

Thanks Mohamed

now in real SP design do they normally run both PE-PE and P-P TE Tunnles ?

I know it is a design choice but if both are required fast convergence within the core and Diffserv/CoS per customer for example

[Mohamed Sobair]

Hello Marwan,

As you said, its a design choice, but In real SP design , they normally have TE from PE-PE rather than P-P.

They utilize it for both SLAs with customers and routing decisions for the un utilized paths, besides faster convergence indeed!

The QoS MPLS is independant from having traffic enginnering or not, You can have QoS withing your MPLS network whether you have TE or not.

Regards,

Mohamed

[Marwan ALshawi]

by the way FYI

Two proposed signaling mechanisms for MPLS traffic engineering are being considered by the IETF’s MPLS work group

– RSVP (Cisco and a number of Gigabit router startups (Avici, Argon, Ironbridge, Juniper, and Torrent))

– CR-LDP (Ericsson, Ennovate, GDC, Nortel)

[Vivek Ruhil · Accepted solution]

Hi

See answers inline:

- When to use MPLS-TE signaling as RSVP vs LDP and why in each case

  >>>>   MPLS-TE is implemented using RSVP in Cisco and is also widely deployed, because RSVP gives you the benefit of on-demand label allocation and also helps in resource reservation. LDP cannot do resource reservation.

- When to use the TE between PEs and to use it between Ps in an SP network and each case what is the recommend signaling RSVP or LDP

e.g for VOIP to be placed in TE using DS-TE with CBTS is it better to have the TE between PEs, if yes when we need it between Ps )

>>>>> This was answered in an earlier post, but just to add now a days, the mostly deployed is One-Hop tunnels between every router with FRR for fast convergence and ofcourse if an SP wants source based routing or DS-TE then PE tunnels are created.

- Can we have mix of TEs between PEs and between Ps ? when this is useful ?

>>>>> Yes ofcourse.

- Auto FRR vs manual

   >>>> Always Auto. You would want the tunnels to go into FRR automatically rather than have to interfere in it.