On 2026-01-21 07:49, Muhammad Atif Jauhar via cisco-nsp wrote:
Greetings,
We are planning to deploy two WAN links from different Service
Providers,
both offering MPLS connectivity with BGP peering. As part of the
design
review, we would like to align on the best-practice approach to
ensure
a
stable, loop-free, and predictable routing architecture.
Given the use of multiple MPLS providers with potentially different
latency
characteristics, our key objectives are to avoid routing loops,
prevent
asymmetric traffic issues, and ensure controlled traffic engineering
and
failover behavior.
Any recommendations or considerations based on your experience,
particularly with respect to MPLS interconnects and BGP traffic
engineering.
Sounds like you have an enterprise network connecting to NSPs. Your
network is probably not an NSP network itself.
It's not strictly on topic for this mailing list, but I'll provide
what's worked well for me.
Use a different RFC6996 private ASN for each site.
If you're doing a green-field deployment, use 10/8 RFC1918 space.
Assign
a /16 to each site, so your second octet becomes your site prefix, and
your VLANs become your third octet.
Choose one NSP as primary, the other as backup. At each site, on your
incoming route policy from the primary NSP, set all routes to high
localpref, say, 1000. Set all routes from secondary provider to a
lower
localpref, say 900.
Use BFD with BGP for fastest failure detection. Ask your carriers to
enable it on your BGP sessions if they support it. There are two
settings with BFD, minimum interval and multiplier. Review those
settings to see what fits your needs best. Detail here:
https://www.cisco.com/c/en/us/td/docs/ios/12_0s/feature/guide/fs_bfd.html
Within each site, install two CE routers. Connect Router A to your
primary NSP, router B to the secondary. Connect the two routers
together
back-to-back and configure iBGP across that link. Be sure to set
next-hop-self on the neighbor.
Pick two hub sites; one a primary site, the other a secondary site.
Set
up the hub sites to announce all routes including those from the spoke
sites. Have the spokes announce only locally originated routes.
Connect those routers to the LAN in each location. Think about how
you'll integrate routing with your LAN gear.
* If you use an IGP internally at any site, avoid routing loops by
taking care not to redistribute locally originated routes from BGP
back
into your IGP.
* If you use static routing, make sure a FHRP is set up on the CEs to
provide failover.
Consider setting up VPN backup through GREoIPSec or VTI tunnels to
your
two hub sites. Run BGP across those tunnels, same BGP process as you
use
for connecting to your NSPs.
Use front-door VRF and ACLs to secure the Internet-facing interfaces
on
the routers.
For routes received via VPN to the primary hub, set those to even
lower
localpref, say 800.
For VPN to the secondary hub, set those to lowest localpref, say 700.
If you have any back-door links between sites, like Metro Ethernet,
switched Ethernet, or optical waves, integrate those by using BGP as
well. Announce locally originated routes with a higher local
preference
than the MPLS networks, say, 1100.
But be careful sharing WAN routes learned via MPLS across a backdoor
link. Don't set those to a higher local preference than the MPLS
network
itself. Avoid if possible.
Also, don't forget about the key management aspects for routers:
syslog,
AAA / TACACS, availability and performance monitoring (SNMP), NTP,
Netflow, and FTP repository for router code. Use a loopback IP on each
router for your management traffic. Avoid SFTP or SCP to your code
repo
due to known performance issues with OpenSSH and file transfers.
Consider setting up out-of-band access. Best is to build a small
parallel WAN/LAN over VPN with a firewall, LAN switch, and serial
console server. Get a separate Internet connection for the firewall
(business broadband works), and use it only for out-of-band access.
If you decide to configure QOS over the WAN, try to use standard
packet
markings like EF for voice media and AF31 for signaling. Check with
your
providers on what markings they support. The less re-marking of
traffic
you have to do, the better.
Regards,
Atif.
Hope all this made sense. I'm happy to clarify anything.
This config served me well in my enterprise days and later on as an
NSP
integrator. 25 years of experience in those spaces.
Hope this helps,
-Brian
