Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
New Member

Trouble with MPLS and P router


This is my first post here so please bear with me carefully. I'll be glad to supply additional information and configs as needed. As a little background, I've done my CCNA last year and am working currently as a tier 1 support technician on an israeli ISP (BZQ). I'm scheduled to do the ROUTE exam this month and am studying for the MPLS + BGP exam. Now for the question.
I've configured a basic topology in GNS3 with 2 PE routers, 1 P router and a CE for every PE. The protocol running PE-CE is RIP configured for VPN, with redistribution into MP-BGP. The IGP in the core is OSPF. When I connect the PE's directly I get ping from CE to CE, but when I connect them through the P router I can't seem to get connectivity even though I do get the correct routes on both CE's, which means BGP is configured correctly and redistributing. When I check the mpls forwarding-table on the P router I see only labels towards the loopbacks of the PE's and no entry for the tag which I see on the PE's ( tag 20).
Does anyone have an idea how should I troubleshoot this issue? I've gone through the MPLS and BGP configuration for both the PE's and P and I've found nothing. I've even tried changing the source of the BGP updates but to no avail.
Thanks in advance for any assistance

Everyone's tags (4)

Trouble with MPLS and P router

Few things for MPLS VPN:

MPLS VPN Troubleshooting:

1. Routes are not showing up in PE VPNv4 table

            1. Check for RT under VRF configuration of LOCAL ROUTER and REMOTE ROUTER

            2. Check for the VRF IGP to BGP VRF address family redistribution on REMOTE ROUTER

            3. Check for the NEXT-HOP-SELF configuration in IBGP or EBGP configuration of REMOTE router

4. Check the REMOTE ROUTER IP ROUTE VRF table or CE-PE routing protocol configuration on REMOTE ROUTER.

            5. Check for VPNv4 session between the REMOTE and LOCAL Router

                        a. check for proper neighbor configuration

                        b. check for update-source if BGP is between LOOPBACK addresses

                        c. Check for ebgp-multihop configuration (MPLS VPN option C)

                        d. Check the activation of neighbor under BGP address-family configuration

                        e. Check if you need local-as configuration option

            6. Check for CE-PE configuration on both end if BGP is the CE-PE protocol

As BGP use different way to advertise the routes and each one need specific component in routing or bgp table

                        1. Network command

                                    a. Network command only

b. Network command with mask (Needs specific component in Routing table of same mask, use static route to achieve this)

                        2. Aggregate command (Need component in BGP table)

3. Redistribute static/connected/IGPs (Check for prefix-list or route-map associated with that)

4. Check neighbor configuration command syntax for Prefix-list or route-map configuration

                        5. Allowas-in on CE routers and AS-OVERRIDE on PE routers

                        *7. no BGP Route-target filter                        

2. Routes are not showing up in CE Routing table

                        1. Check for the next-hop info in VPNv4 table of LOCAL ROUTER and in IP Routing table

                        2. Check for redistribution of BGP routes into the CE-PE table of local PE

                        3. Check for passive interface config on both PE and CE routes

                        4. Check for area connectivity in OSPF and configure Virtual link if needed

                        5. Check for CE-PE protocol version configuration in case of RIP

                        6. Check for BGP configuration

3. Ping ISSUE

                        1. Most of the issue is broken LSP

                                    a. Check for IP CEF is enabled or not

                                    b. Label distribution protocol mismatch LDP or TCP

                                    c. Make sure label protocol is enabled globally as well as on interface

                                    d. look at the LOOPBACK updates in IGP as well as label allocation for it

                                                Configure OSPF loopback with point to point network type


                                                Use loopback of /32

                                    e. check for end to end LSP using

                                                CEF table

                                                MPLS Forwarding Table


                                                BGP VPNv4 table with label

f. In MPLS VPN option B (Here BGP next hop will do the work, you can avoid the redistribution)   and C don’t forget to redistribute the BGP into IGP to generate the label for remote AS PE's LOOPBACK's in local AS ,  same way advertise local AS PE's loopback to the remote AS.

g. Check for MPLS configuration between both the AS if you are using the Option B with Multihope MP-EBGP between the  loopback interface of ASBR's of two different PE's of respective AS.

4. Desire Path for traffic:

            a. next-hope-unchange (MPLS VPN option C)

            b. Local Pref on local router

            c. MED on remote router

            d. redistribution with different metrics on differnet PEs facing to same Cutomer's CEs

            e. OSPF SHAM-LINK with metrics manipulations

5. Loop prevention in MPLS VPN:

            a. BGP uses SOO

                        Use with route-map

                        ip vrf sitemap

            b. EIGRP uses SOO

                        ip vrf sitemap

            c. OSPF uses DOWN-BIT (LSA-3) & TAG-BIT (LSA-5 & 7)

CreatePlease to create content