MPLS static route

Answered Question
Mar 11th, 2010

Hello Experts,

Diagram: Carrier supporting Carrier.

CE- A  --------PE-1(DIST)-------PE(CORE)--------PE(ISP)-----P-------PE-------CE-B

                                                      |

                                                      |

                                                   PE-2(DIST)    CE-A is also connected to PE-2

I m pointing a static route towards CE-A router for his network.On PE(DIST) router I m redistributing the static route in BGP to be reach for another end of the customer CE-B.WHen i disconnect the cable from my PE(DIST) router heading to customer A,the static route disappears in VRF table from the PE(CORE) why that so.???. Actually the route disappears is good but i want to know the reason?? In traditional static route the route does nt disappears from the routing table so we shld have such mechnasim of IP SLA.

I have a redundant connection for customer A on another distribution switch (i.e is not shown in the diagram) the route from PE-2 is chosen whenever i remove the cable from the PE-1.

Thanks

I have this problem too.
0 votes
Correct Answer by Giuseppe Larosa about 6 years 9 months ago

Hello Andy,

my first answer was incomplete so ignore the line that you could not understand.

>>>In global routing table the same can happen or not??

as Reza has pointed out, if there is a direct cable between PE and CE node as soon as the cable is unplugged PE interface in VRF goes down and the static route is removed detecting the IP next-hop is not reachable anymore.

if there is a lan switch in the middle when you unplug the cable on CE side PE interface does not go down and the node can detect the CE is not available when the ARP entry expires and it has to perform a new ARP request for CE IP address.

Up to 4 hours with default ARP timeout value!

It is a big difference and it one of reason I recommend using a dynamic protocol in lan switched environments or at least to track next-hop reachability with reliable static routing.

About redistributing connected in VRF:

some years ago we had an issue that we solved by using redistribute connected (without it CEF entries were not correct for static routes in VRF).

It does not cause any problem and allows for:

- pinging  CE interface from another VRF site

- exporting of connected VRF access link to a management VRF for SP managed CE nodes.

Hope to help

Giuseppe

Correct Answer by Reza Sharifi about 6 years 9 months ago

thomasandy32 wrote:

Hello Giuseppe

i have pointed a simple static vrf route with a  IP address of the customer as a next-hop.

ip route vrf cust-A 10.25.25.X  255.255.255.0 10.1.1.1

Is it this usual in mpls the static route disappearing from the route table??

One thing more i want to post,i have redistributed the connected interface between the CE and the PE routers.

>>>In global routing table the same can happen or not??

I did nt understood ur above line in previous mail.

Hi,

The static route disappears, because you unplug the cable.  Also, your static route towards cust-A is correct.  The only thing I don't understand is why you are redistributing connected interfaces on the CE router.  You usually don't need to do that, because most of the time the customers do not want to advertise all connected routes to the provider.  You usually deploy a static route or a default route toward your service provider.

HTH

Reza

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Giuseppe Larosa Fri, 03/12/2010 - 06:56

Hello Andy,

>> Actually the route disappears is good but i want to know the reason?

when cable is unplugged connected interface in VRF goes down the static route is removed from VRF IP routing table and BGP stops to advertise the IP prefix into BGP ( address-family vrf VRF-name and vpnv4 towards other backbone devices).

Have you added the interface name as an option  in the ip route vrf command ?

In global routing table the same can happen or not

Hope to help

Giuseppe

thomasandy32 Fri, 03/12/2010 - 11:55

Hello Giuseppe

i have pointed a simple static vrf route with a  IP address of the customer as a next-hop.

ip route vrf cust-A 10.25.25.X  255.255.255.0 10.1.1.1

Is it this usual in mpls the static route disappearing from the route table??

One thing more i want to post,i have redistributed the connected interface between the CE and the PE routers.

>>>In global routing table the same can happen or not??

I did nt understood ur above line in previous mail.

thomasandy32 Sat, 03/13/2010 - 12:50

Hello Giuseppe,

Any update for the above mail.

The removal of static route from the routing table is normal or any misconfiguration from my end.

Thnaks.

Correct Answer
Reza Sharifi Sat, 03/13/2010 - 21:09

thomasandy32 wrote:

Hello Giuseppe

i have pointed a simple static vrf route with a  IP address of the customer as a next-hop.

ip route vrf cust-A 10.25.25.X  255.255.255.0 10.1.1.1

Is it this usual in mpls the static route disappearing from the route table??

One thing more i want to post,i have redistributed the connected interface between the CE and the PE routers.

>>>In global routing table the same can happen or not??

I did nt understood ur above line in previous mail.

Hi,

The static route disappears, because you unplug the cable.  Also, your static route towards cust-A is correct.  The only thing I don't understand is why you are redistributing connected interfaces on the CE router.  You usually don't need to do that, because most of the time the customers do not want to advertise all connected routes to the provider.  You usually deploy a static route or a default route toward your service provider.

HTH

Reza

thomasandy32 Sun, 03/14/2010 - 03:59

Hello,

I m just redistributing the connected interface for testing purpose nothing else, so the conclusion for the thread is:

Conclusion:

In MPLS Network's VRF static routes pointing to the customer destination will disappears by default when the data-link layer between the CE and the PE goes down.

AND

In traditional static route's they does'nt disappear from the routing table for that we shld have such mechanism like IP SLA and track command on static routes.

Please correct me if the above statement are wrong or any misunderstanding by me.

Thanks

Correct Answer
Giuseppe Larosa Sun, 03/14/2010 - 03:57

Hello Andy,

my first answer was incomplete so ignore the line that you could not understand.

>>>In global routing table the same can happen or not??

as Reza has pointed out, if there is a direct cable between PE and CE node as soon as the cable is unplugged PE interface in VRF goes down and the static route is removed detecting the IP next-hop is not reachable anymore.

if there is a lan switch in the middle when you unplug the cable on CE side PE interface does not go down and the node can detect the CE is not available when the ARP entry expires and it has to perform a new ARP request for CE IP address.

Up to 4 hours with default ARP timeout value!

It is a big difference and it one of reason I recommend using a dynamic protocol in lan switched environments or at least to track next-hop reachability with reliable static routing.

About redistributing connected in VRF:

some years ago we had an issue that we solved by using redistribute connected (without it CEF entries were not correct for static routes in VRF).

It does not cause any problem and allows for:

- pinging  CE interface from another VRF site

- exporting of connected VRF access link to a management VRF for SP managed CE nodes.

Hope to help

Giuseppe

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