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khee
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BGP dual home best practice

Thu Apr 07, 2022 8:06 pm

some doc. about it is needed to migrate from static to BGP because of scalability
 
eduplant
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Re: BGP dual home best practice

Thu Apr 07, 2022 10:08 pm

Some questions:
  1. Do you have some specifics about what your network currently looks like? Hopefully a diagram?
  2. Do you have provider-independent address space?
 
khee
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Re: BGP dual home best practice

Fri Apr 08, 2022 9:10 pm

1. yes, it's basically dual homing from the ISP to the customer on v7.1.5 and I don't know how to insert diagram.

2. yes, it's between private ASs from the ISP standpoint and some private address used.
 
eduplant
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Re: BGP dual home best practice

Fri Apr 08, 2022 10:26 pm

I don't know how to insert diagram.
In the post UI there's an Attachments tab next to Options where you can upload images. Once they're uploaded, you can also place them inline. Seeing a diagram would be a big help.

1. yes, it's basically dual homing from the ISP to the customer
Same upstream ISP, just more than one link for redundancy?

2. yes, it's between private ASs from the ISP standpoint and some private address used.
By private addresses do you mean addresses you got assigned from the ISP (provider-aggregatable)?
 
khee
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Re: BGP dual home best practice

Fri Apr 08, 2022 11:18 pm

diagram attached and thinking about using as prepending. And just to clarify, I am the ISP Engineer on top of diagram and bottom is CE.
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eduplant
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Re: BGP dual home best practice

Sat Apr 09, 2022 12:21 am

And just to clarify, I am the ISP Engineer on top of diagram and bottom is CE.
Ah okay, that helps also. I usually assume people asking are the downstream customers.

So looking at the diagram ... you are sharing RFC 1918 space with a downstream customer? They're not announcing you any public address space they're just supposed to be announcing the 106 and 103 LANs from the left side and the 102 and the 105 LANs from the right side?

Is the customer network contiguous? The diagram seems to imply that they are fully reliant on your network to get between their sites. If that's the case then they're not so much multihomed.

This is a little irregular for what I would typically expect and I'm trying to get a better handle on the overall goals before I make any suggestions.
 
khee
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Re: BGP dual home best practice

Mon Apr 11, 2022 4:39 pm

I think the attached has better diagram.

The main purpose is the ISP on the upper side is using floating static route to customer's private and public IP networks.

But, that only works when the primary link goes down.

And the customer wants some of their private or public IP networks goes down through the primary, they want automatic switchover to secondary connection.

So the customer would like use BGP in between private IPs & ASs and want us to use route-map for weight or something else.

Is it doable ?
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eduplant
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Re: BGP dual home best practice

Mon Apr 11, 2022 9:50 pm

  1. What do the red lines represent?
  2. Are each of the 7 firewall icons a different customer or different sites for the same customer?
  3. Where do the public addresses come into play? Are they PI or PA addresses? Are you already announcing them to the rest of the world via BGP?

Some version of this is probably doable but exactly what depends on the details. If they just have one site and it’s multihomed, then two of your routers will speak eBGP with their router and you can arrange with them to either respect their MEDs or they can prepend. Make sure you write appropriate filters so that you will only accept what you expect them to announce.

Whether you want to announce them a default route and let them localpref their preferred path or whether you want to announce them a selection of more specifics will depend on a) whether you have full or partial tables yourself or b) whether it will do them any good. If all of their traffic is funneled through Vienna anyway, then there isn’t much of a path choice for them to make and you should just announce a default.
 
khee
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Re: BGP dual home best practice

Mon Apr 11, 2022 10:03 pm

1. Link to CE Cisco Router
2. Yes, Branch CE Cisco Router for same customer
3. most customer public IP Networks and I assume that they use it for internet access.
Default route is not preferred because only 1 of 8 of their public IP networks not reachable through primary in that case BGP automatically switchover only to that route to lower MED or else.
I think the big hurdle for the customer is advertising those 8 public IP networks to us via eBGP. and I assume that customer engineer is not an expert in BGP, so maybe minimum configuration can be done.

I attached the full diagram.
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eduplant
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Re: BGP dual home best practice

Mon Apr 11, 2022 10:52 pm

And are the blue and grey lines also physical links? This would mean CE router #3 from the left would have … 6 uplinks? If just counting red that would be 4?

Default route is not preferred because only 1 of 8 of their public IP networks not reachable through primary in that case BGP automatically switchover only to that route to lower MED or else.

Oh so is this concern more about their intersite connectivity than their connectivity to the internet? If their AS path for their “internal” routes is going to be 65106,65000,65105 on your diagram (this would be Moultrie to Tifton North I think), then the best path would be Tifton 2nd St because it doesn’t have to traverse the path to Vienna. (Also I’m making up that your ISP AS here is 65000; I don’t think you specified.)

This is going to involve a lot of manual policy work on your part because BGP is going to inherently hide all of the topology details of your network. What you could do is to set up a series of BGP communities that correspond to the ingress router, so say 65000:1 is routes learned from peers on Tifton 2nd St, 65000:2 is learned from peers on Tifton 4th St, etc. You can then build a routing policy for each of your routers that will announce the lowest MED for routes that originated on that router and then a higher MED for any other routes.

The customer would then receive from each upstream peer: 1) a default route (for internet traffic) and 2) all of their own routes from other sites with two possible MEDs. In the token example, as long as Moultrie still has a link up to Tifton 2nd St, they will see and use the lowest MED down that path to Tifton North. If that whole path fails then they will still have a route to it via any of their other uplinks.

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