MPLS - BGP

[anthony.dyne]

Hi

Seeking MPLS (BGP)  assistance,

MPLS on "B" will be up soon.

(( A )) ----( Fiber_connection )------------ (( B ))

   |                                                                    |

   |                                                                    |

   |                                                                    |

   |                                                                    |

   |                                                                    |

   ========MPLS======================

                        ||

                        ||

                     (( C ))

A connects to B over Fiber

A also connects to service Provider MPLS Cloud with 5MB Bandwidth

B also connects to service Provider MPLS cloud with 5MB Bandwidth

C connects to to service Provider MPLS cloud with 1 MB Bandwidth

MPLS service is running BGP

OSPF is running on LAN Segment

On "A" and "C" we got mutual redistribution between OSPF and BGP

C needs Email/Application traffic from A and Voice/Intranet from B.

Question : 1
can I route Email/Application traffic from C to A and Voice/Intranet traffic from C to B

(((((  without MPLS Service provider involvement    ))))

Question: 2

How do I manage the traffic from A to B to take Fiber as the Primary connection and MPLS connection as Backup route.

MPLS will be backdoor ; how to control routes entering and existing on "A" and "B"

[Giuseppe Larosa]

Hello Anthony,

>> This one is really Stupid ONE " Please Reply"

I would like to clear one basic question, "When do mutual redistribution is  needed"

mutual redistribution is needed when using default routes is not possible.

In your scenario you can use network commands in BGP proceess, instead of redistribute ospf into BGP if the number of IP prefixes is less then 200 that is the maximum number of network statements you can use.

If the total number of IP subnets in Site A and Site B is less then 200 you can skip redistribution of OSPF into BGP on MPLS router A and MPLS router B.

You can keep redistribution of BGP into OSPF if you need the details of Site C routes and you cannot be happy with a default route injected in OSPF domain by MPLS router A and MPLS router B.

this greatly simplifies as you don't need to go with route tagging and route maps anymore

The same reasoning can be applied on MPLS router C

>> I need to take these steps

• a) On Mutual redistribution Point  -->> Apply filter ( I would use tagging )
  
• b) Add network statement in BGP Process with correct mask

No, or you do a) or you do b) you don't need both sorry if I have been unclear

Hope to help

Giuseppe

[milan.kulik]

Hi,

I agree with Giuseppe, if the topology is not so complicated, keeping BGP redistributed to OSPF with his a) or b) proposal is the easiest way.

Another possibility might be asking the provider to avdertise a default route conditionally in a case the PE-CE BGP session is Up only and redistributing the default route only to the OSPF. You would need no static then and would not create a black-hole routing in a case of a BGP session failure.

But for your topology this would be too complicated, I'm afraid.

BR,

Milan

[anthony.dyne]

Thanks for supporting the post.

One Last question

The Network which is needed by Site "C" needs to be advertised in BGP Process on "A" && "B"

Any action needed on "C"

[Giuseppe Larosa · Accepted solution]

Hello Anthony,

if site C contains only router MPLS C no additional actions are needed, otherwise you can think of redistributing BGP routes into Site C MPLS C CE OSPF router process.

The service provider can easily accomodate for the use of same private AS number in all of your sites by using as-override so your CE MPLS C router shouldn't need any special BGP trick to accept routes coming from Site A and/or Site B.

(if the SP would not override the AS number, your router would not accept a BGP route with an AS path that already contains its own AS number and would silently discard it for the eBGP loop avoidance rule).

To be noted for this router the BGP next-hop is PE C router IP address you will not be able to know what is the chosen best path by examining the BGP advertisements received on SIte C CE node.

Hope to help

Giuseppe

[anthony.dyne]

Thank both Experts for the excellent support.

[antasson]

Hi Anthony,

my answers inline:

>Question : 1
>can I route Email/Application traffic from C to A and Voice/Intranet traffic from C to B

>(((((  without MPLS Service provider involvement    ))))

No, unless you don't build GRE tunnels and run an IGP over them

>Question: 2

>How do I manage the traffic from A to B to take Fiber as the Primary connection and MPLS connection as Backup route.

>MPLS will be backdoor ; how to control routes entering and existing on "A" and "B"

Just configure OSPF over the backdoor link. The routes that are redistributed from BGP to OSPF on A, won't be redistributed back to BGP in C because of the automatic checks on the tags C will do.

This way between A and C you'll use the backdoor link.

Best regards,

Antonio

[anthony.dyne]

Hi

As per Cisco SE  "When you got more than one mutual redistribution point then you need to filter the updates either using TAG or other methods"

I would like to clear one basic question, "When do mutual redistribution is needed"

Lets take an example

HQ connects to Branch-Office using service Provider MPLS Cloud

• HQ is hosting all Services Email / Application / Intranet-Portals.
• Branch offices gets all its services from HQ
• At Branch office there is Domain controllers,Backup_Servers which needs to replicate with domain controllers at HQ
• Admin in HQ needs to access Servers/Users Pcs in Branch_Offices for Troubleshooting and Maintenance.

For the above needs do I need to have Mutual Redistribution.

For LAN OSPF is used as routing Protocol

For WAN BGP is used as routing protocol ( config is provided by SP )

Here is a sample config of Service_provider

interface FastEthernet0/0
no ip address
duplex auto
speed auto
!
interface FastEthernet0/0.34
encapsulation dot1Q 34
ip address 172.31.31.138 255.255.255.252
!

router bgp 65001
no synchronization
bgp log-neighbor-changes
  neighbor 172.31.31.137 remote-as 65000
no auto-summary

{ Neighbor 172.31.31.137  - Service Provider next hop }