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AdrianT88
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Default Route forwarding via eBGP

Wed Oct 14, 2020 6:05 pm

Hi all,

We operate a small WISP environment where each tower/bldg. rooftop utilizes a CCR1036. Some towers have fiber PtP towards to the core, and the towers without fiber access utilize mmWave PtPs to the nearest fiber lit buildings as the next hop. I am running eBGP towards the core and between all the tower peerings. The CCRs that peer with the core (Juniper QFX5100) receive a default route and I am trying to understand if the CCR1036s forward the def route to other towers only if "default originate / if installed" is enabled.

I attached a diagram that illustrates this a little more. Would I need to enable default originate on all the CCRs to accomplish the following? Can the CCRs just forward the def. and then I can manipulate the paths via local pref/weight? I don't see how this will work if for example Towers 3 & 4 originate def. routes to each other.

Tower3 paths:
-primary path through Tower2
-secondary path through Tower4 and 5

Tower4 paths:
-primary path through Tower5
-secondary path through Tower3 and 2

Thanks,
-AT
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mrz
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Re: Default Route forwarding via eBGP

Thu Oct 15, 2020 10:39 am

Default route is special case, you will need to enable default-originate on all routers along the path to advertise default route.
 
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IPANetEngineer
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Re: Default Route forwarding via eBGP

Thu Oct 15, 2020 4:18 pm

Yes, you'll need to enable default-originate (if installed) on all peerings in this type of design. I would use BGP communities to set either weight or localpref

I did a presentation a few years ago on this type of design at the US MUM in Denver. Here is an overview of the way we used communities. eBGP for WISP traffic engineering has become more and more popular in the last few years.

https://mum.mikrotik.com/presentations/ ... 062656.pdf

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AdrianT88
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Re: Default Route forwarding via eBGP

Fri Oct 16, 2020 6:56 pm

Default route is special case, you will need to enable default-originate on all routers along the path to advertise default route.
Thanks for your reply mrz. After running some more tests, I would have to agree that default originate has to be enabled on all the routers. Is there anything else I need to be aware of or configure in order to avoid any routing loops given the fact that each router will advertise a default to each other?

Thanks,
-AT
 
AdrianT88
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Re: Default Route forwarding via eBGP

Fri Oct 16, 2020 7:45 pm

Thanks IPANetEngineer. I actually came across that presentation as I started working with Mikrotik devices. At the time, I didn't think using bgp communities would enable my network to have the most efficient traffic engineering and redundancy. I currently have 7 active buildings that have a direct 10G or 1G fiber PtP towards my core. I have another 5 buildings that use mmWave PtP to the nearest fiber lit building. The eBGP Wisp presentation illustrates that there are only 2 paths - "northern and southern" coming out from Tower-1. I feel like I could use the same design if only two of my towers have PtPs to the core and the rest of the towers would connect to Tower1 or 2. I could then use bgp communities and influence traffic over only two separate paths.

At the moment, not every tower in my network has two separate paths towards to the core or to another building, and then some buildings are part of mini-rings involving 3 or 4 towers as shown in my diagram. I was planning on having each Mikrotik that connects to the core receive and forward the default to its peers and then using local-pref/weight on each router for path manipulation. My biggest concern is creating loops by enabling default-originate on every router when they are connected to each other and distributing the defaults towards themselves. Each router has separate inbound and outbound filters for every neighbor.

Thanks,
-AT

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