[c-nsp] BGP Route Announcement

[Randy]

...you mean a floating-static to Null0 with a distance of 254?; especially when prefix-lengths are the same(what is in IGP and what is being advertised)so the internet doesn't burble if your IGP does?

Observations for OP:

1) As has been mentioned: please migrate to prefix-lists.
2)Looking at your posted-config:
a)There is *no* need to have a prefix-filter/distribute-list and a route-map in place for your upstream. Since you already have a route-map in place for inbound&outbound to your ISP; you can have your route-maps do everything for you.
b)There is Zero-Value in having *soft-reconfig-inbound* for your session with your ISP(this is 2018 and I dare say, every BGP speaker supports soft-reset in/out!

*soft-reconfig* makes sense on Customer-Sessions; if you are an ISP(so you can prove to customer "what-you-are-receiving" prior to any-modification by your router; to end the "This-is-Your-Problem" issue.

-Randy






________________________________
From: Bryan Holloway <bryan at shout.net>
To: Cisco Network Service Providers <cisco-nsp at puck.nether.net> 
Sent: Friday, December 14, 2018 3:37 PM
Subject: Re: [c-nsp] BGP Route Announcement



I generally prefer to keep the Null0 even if there's a static or (IGP) 

non-static as a matter of best-practice.


If your IGP burbles, then the rest of the Internet won't, leading to 

faster recovery times.


Statics are inherently less prone to this, but having the Null0 pin-up 

doesn't hurt anything and it makes your configuration more homogeneous 

knowing that anything you're advertising should be in the routing table 

no matter what. Easier to trouble-shoot, spot errors, etc.



On 12/14/18 2:40 PM, Shawn L wrote:

> That second part has bit me in the rear before..... As a matter of course

> now I always make a static route to null 0 for every prefix I announce via

> BGP.  Once I verify that an IGP or static route is covering that prefix, I

> remove the null route.... or not if you have several more specific routes.

> 

> On Fri, Dec 14, 2018 at 12:34 PM Mark Tinka <mark.tinka at seacom.mu> wrote:

> 

>>

>>

>> On 14/Dec/18 19:16, Joseph Mays wrote:

>>

>>>

>>> The distribute lists shown also just contained appropriate permit and

>> deny entries for 216.24.0.0 /18

>>

>> Firstly, please don't use distribute lists. This is very archaic and

>> prone to mistakes. Suggest you migrate to prefix lists right away!

>>

>>>

>>>

>>> That changed the broadcast cogent was receiving, but not in the expected

>> way. They only route they saw us broadcasting after that was the

>> 216.24.60.0/23 route. Not the first one in the list, not the last one,

>> not the biggest one or the smallest one, but just one route from the middle

>> of the list. I don't get this behavior at all. Cogent cleared and bounced

>> bgp to us, and still received only that one route in the broadcast from us.

>>

>> After you've fixed your filtering with prefix lists, you need to ensure

>> that any "network..." statement is backed up by the presence of the very

>> same route in your IGP (which includes static routing).

>>

>> Mark.

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