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BGP full mesh throughput question

dhananjay95929
Level 1
Level 1

I have couple questions regarding a BGP full mesh topology. Please refer to the diagram below. Each depicted link on routers R1 to R4 in AS 100 only is actually a port-channel of two physical 10G links.

The questions I have are as follows:

Scenario 1:

If NO full mesh iBGP between R1,R2,R3,R4 and maximum-paths command configured:

  • What is the throughput that AS 100 is able to send traffic towards AS 200?
  • What is the throughput that AS 100 is able to send traffic to AS 200 when one 10G link in lets say one of the port-channel's (could be any one) in AS100 is down?

Scenario 2:

If full mesh iBGP between R1,R2,R3,R4 and no maximum-paths command configured:

  • What is the throughput that AS 100 is able to send traffic towards AS 200?
  • What is the throughput that AS 100 is able to send traffic to AS 200 when one 10G link in lets say one of the port-channel's (could be any one) in AS100 is down?

The assumption is that AS 100 is utilizing all 20G links on all routers in AS 100 to their full capacity.

Scenario 1: no iBGP full-mesh and "maximum-paths 4" command configured under BGP

Scenario 2: iBGP full mesh in AS100 and no "maximum-paths 4" command configured under BGP

2 Accepted Solutions

Accepted Solutions

Joseph W. Doherty
Hall of Fame
Hall of Fame

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages wha2tsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

What is the throughput that AS 100 is able to send traffic towards AS 200?

I believe, by default, BGP will only use one link, per router, between AS 100 and AS 200; so maximum possible throughput would then be 4 x 20g, or 80g.  Of course, other factors affect actual maximum throughput, i.e. how traffic is sent to R1..R4 and how flows are distributed across the Etherchannel links.

With a BGP config set to use all logical links, maximum throughput would be 4 x 80g, or 320g.

What is the throughput that AS 100 is able to send traffic to AS 200 when one 10G link in lets say one of the port-channel's (could be any one) in AS100 is down?

Zero to 10g less.  Traffic on the Etherchannel would only have one link to use, but insufficient information to say whether that Etherchannel was carrying any traffic or whether other Etherchannel link was carrying any traffic.

View solution in original post

ahmedshoaib
Level 4
Level 4

Hi;

As per your requirement please find below are my observation:

  1. BGP Load Sharing When Dual-Homed to One Internet Service Provider (ISP) Through a Single Local Router: (Consider R1 – R4 are different site in AS100)

We can achieve load sharing when multiple links exist between a remote AS and a local AS. These links are terminated in one router at the local AS and on multiple routers at remote ASs in a single-homed BGP environment via maximum-paths feature. By default, BGP chooses one best path among the possible equal-cost paths that are learned from one AS. However, you can change the maximum number of parallel equal-cost paths that are allowed (1-6).

 

Q 1 – Throughput from AS 100 to AS 200.

Ans – You can achieved throughput from each RTR 20x4 = 80 (in case of equal cost) & from AS100 it will be 80x4 = 320G

 

Q 2 – Throughput from AS 100 to AS 200 (if 1 link is down of port-channel).

Ans – In case the whole port-channel is out of the network due to the cost will be change.

E.g R1 will have 3x20= 60 instead of 80 in case of 1 port is down of port-channel.

 

  1. Load Sharing When Dual-Homed to One ISP Through Multiple Local Routers: (Consider R1 – R4 are on same site in AS 100)

We can achieve load sharing when there are multiple connections to the same ISP through multiple local routers. The two eBGP peers are terminated on two separate local routers. Load balancing on the two links is not possible because BGP chooses the single best path among the networks that is learned from eBGP and internal BGP (iBGP). Load sharing among the multiple paths to AS 100 is the next-best option calculating via BGP attribute.

 

Q 1 – Throughput from AS 100 to AS 200.

Case 1 – If RTR in AS100 are in same side & RTR in AS200 are in different site

Ans – In this case you are also running iBGP or IGP protocol b/w R1-R4 in AS 100. Only 1 Router will be selected for best path either via automatically or manually playing with BGP attribute. You can achieved throughput from AS-100 to AS-200 20x4 = 80 (in case of multipath feature is enable)

 

Case 2 – If RTR in AS100 are in same side & RTR in AS200 are also in same site)

Ans – In this case you are also running iBGP or IGP protocol b/w R1-R4 in AS 100 & AS 200. Only 1 Router will be selected for best path either via automatically or manually playing with BGP attribute. You can achieved throughput from AS-100 to AS-200 is 20G.

 

Q 2 – Throughput from AS 100 to AS 200 (if 1 link is down of port-channel).

Case 1 – If RTR in AS100 are in same side & RTR in AS200 are in different site

Ans – In this case you are also running iBGP or IGP protocol b/w R1-R4 in AS 100. Only 1 Router will be selected for best path either via automatically or manually playing with BGP attribute. Now it’s depend on path/RTR selection can achieved throughput from AS-100 to AS-200 either 60 or 80 (in case of multipath feature is enable)

 

Case 2 – If RTR in AS100 are in same side & RTR in AS200 are also in same site)

Ans – In this case you are also running iBGP or IGP protocol b/w R1-R4 in AS 100 & AS 200. Only 1 Router will be selected for best path either via automatically or manually playing with BGP attribute. Now it’s depend on path/RTR selection can achieved throughput from AS-100 to AS-200 either 10 or 20.

 

Please find the Link below for further detail on BGP Load sharing.

http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13762-40.html#anc5

Thanks & Best regards;

View solution in original post

7 Replies 7

Joseph W. Doherty
Hall of Fame
Hall of Fame

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages wha2tsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

What is the throughput that AS 100 is able to send traffic towards AS 200?

I believe, by default, BGP will only use one link, per router, between AS 100 and AS 200; so maximum possible throughput would then be 4 x 20g, or 80g.  Of course, other factors affect actual maximum throughput, i.e. how traffic is sent to R1..R4 and how flows are distributed across the Etherchannel links.

With a BGP config set to use all logical links, maximum throughput would be 4 x 80g, or 320g.

What is the throughput that AS 100 is able to send traffic to AS 200 when one 10G link in lets say one of the port-channel's (could be any one) in AS100 is down?

Zero to 10g less.  Traffic on the Etherchannel would only have one link to use, but insufficient information to say whether that Etherchannel was carrying any traffic or whether other Etherchannel link was carrying any traffic.

Thanks for your response.

I have a couple of follow up questions:

1. Why would BGP use only one link per router? Are you saying that unless the "maximum-paths 4" command is configured under the BGP process on each router, BGP would only select one best path out of AS100?

2. From your answer to the second question, why do you think it could be from 0 to 10G less and not 10G less only. Why do you think there could be a range from 0 to 10G less. Would the total throughput number be 310G if that etherchannel was carrying 10G full traffic?

The assumption is that all links are being used to full capacity.

Thanks!

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages wha2tsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

#1

Correct.

#2

As I described, don't know whether the failed link had been carrying traffic, as it wouldn't if not using multiple logical links.  If Etherchannel pair not being used, loss of a member link would result in zero bandwidth loss.  If, however, as you posit all links are being used to full capacity, then yes, you would lose 10g.

I updated the original post when there is iBGP full mesh between all four routers in AS 100 and no maximum-paths command configured under BGP under any of the four routers.

Do you agree that it would be 320G maximum possible throughput only when no iBGP full mesh between routers of AS 100 and maximum-paths 4 command configured under BGP on each router?

Thanks!

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages wha2tsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Once traffic gets to AS 100 routers, and as long as there's one logical link to AS 200, the iBGP mesh has no impact.  By default, eBGP routes will be preferred over the iBGP routes.

ahmedshoaib
Level 4
Level 4

Hi;

As per your requirement please find below are my observation:

  1. BGP Load Sharing When Dual-Homed to One Internet Service Provider (ISP) Through a Single Local Router: (Consider R1 – R4 are different site in AS100)

We can achieve load sharing when multiple links exist between a remote AS and a local AS. These links are terminated in one router at the local AS and on multiple routers at remote ASs in a single-homed BGP environment via maximum-paths feature. By default, BGP chooses one best path among the possible equal-cost paths that are learned from one AS. However, you can change the maximum number of parallel equal-cost paths that are allowed (1-6).

 

Q 1 – Throughput from AS 100 to AS 200.

Ans – You can achieved throughput from each RTR 20x4 = 80 (in case of equal cost) & from AS100 it will be 80x4 = 320G

 

Q 2 – Throughput from AS 100 to AS 200 (if 1 link is down of port-channel).

Ans – In case the whole port-channel is out of the network due to the cost will be change.

E.g R1 will have 3x20= 60 instead of 80 in case of 1 port is down of port-channel.

 

  1. Load Sharing When Dual-Homed to One ISP Through Multiple Local Routers: (Consider R1 – R4 are on same site in AS 100)

We can achieve load sharing when there are multiple connections to the same ISP through multiple local routers. The two eBGP peers are terminated on two separate local routers. Load balancing on the two links is not possible because BGP chooses the single best path among the networks that is learned from eBGP and internal BGP (iBGP). Load sharing among the multiple paths to AS 100 is the next-best option calculating via BGP attribute.

 

Q 1 – Throughput from AS 100 to AS 200.

Case 1 – If RTR in AS100 are in same side & RTR in AS200 are in different site

Ans – In this case you are also running iBGP or IGP protocol b/w R1-R4 in AS 100. Only 1 Router will be selected for best path either via automatically or manually playing with BGP attribute. You can achieved throughput from AS-100 to AS-200 20x4 = 80 (in case of multipath feature is enable)

 

Case 2 – If RTR in AS100 are in same side & RTR in AS200 are also in same site)

Ans – In this case you are also running iBGP or IGP protocol b/w R1-R4 in AS 100 & AS 200. Only 1 Router will be selected for best path either via automatically or manually playing with BGP attribute. You can achieved throughput from AS-100 to AS-200 is 20G.

 

Q 2 – Throughput from AS 100 to AS 200 (if 1 link is down of port-channel).

Case 1 – If RTR in AS100 are in same side & RTR in AS200 are in different site

Ans – In this case you are also running iBGP or IGP protocol b/w R1-R4 in AS 100. Only 1 Router will be selected for best path either via automatically or manually playing with BGP attribute. Now it’s depend on path/RTR selection can achieved throughput from AS-100 to AS-200 either 60 or 80 (in case of multipath feature is enable)

 

Case 2 – If RTR in AS100 are in same side & RTR in AS200 are also in same site)

Ans – In this case you are also running iBGP or IGP protocol b/w R1-R4 in AS 100 & AS 200. Only 1 Router will be selected for best path either via automatically or manually playing with BGP attribute. Now it’s depend on path/RTR selection can achieved throughput from AS-100 to AS-200 either 10 or 20.

 

Please find the Link below for further detail on BGP Load sharing.

http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13762-40.html#anc5

Thanks & Best regards;

However, if its full mesh iBGP between the AS100 and no maximum-paths command configured, would the total throughput now be only 20G?

Edit: you already answered that, thank you very much for your detailed response!

Updated diagram:

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