iBGP - Simple static route exchange

Cedric Lemarchand yipikai7 at gmail.com
Wed Mar 1 07:24:25 CET 2017


Bump 

--
Cédric Lemarchand

> Le 25 févr. 2017 à 18:03, Cedric Lemarchand <yipikai7 at gmail.com> a écrit :
> 
> Hello Ondrej,
> 
> Thanks for your precious explanations. Unfortunately I am still stuck, static routes does not apply between 2 hosts.
> 
> To solve 1) and 2), and in the way I only need to publish static routes to other BGP hosts, I changed "export all” by "export where proto = “static1” “,  but still no luck. I notice that static routes are not received any more on hosts.
> 
> Here is my understanding of “show protocol all” on host1 :
> 
> direct1  Direct   master   up     17:35:58
>   Preference:     240
>   Input filter:   ACCEPT
>   Output filter:  REJECT
>   Routes:         2 imported, 0 exported, 2 preferred
>   Route change stats:     received   rejected   filtered    ignored   accepted
>     Import updates:              2          0          0          0          2
>     Import withdraws:            0          0        ---          0          0
>     Export updates:              0          0          0        ---          0
>     Export withdraws:            0        ---        ---        ---          0
> 
> Bird finds 2 direct routes related to eth0 and eth1, so they are received, accepted, but not exported, which is fine.
> 
> kernel1  Kernel   master   up     17:41:12
>   Preference:     10
>   Input filter:   ACCEPT
>   Output filter:  REJECT
>   Routes:         1 imported, 0 exported, 1 preferred
>   Route change stats:     received   rejected   filtered    ignored   accepted
>     Import updates:              1          0          0          0          1
>     Import withdraws:            0          0        ---          0          0
>     Export updates:              6          5          1        ---          0
>     Export withdraws:            0        ---        ---        ---          0
> 
> Bird find 1 static route and try to export 6 routes but they all get rejected or filtered, which is fine too, but I dont know why “6” routes of the routing table bellow :
> 
> root at host1:~# ip r
> 10.10.1.0/24 dev eth0  proto kernel  scope link  src 10.10.1.1
> 10.10.2.0/24 via 10.10.1.254 dev eth0
> 192.168.1.0/24 dev eth1  proto kernel  scope link  src 192.168.1.1
> 
> device1  Device   master   up     17:41:12
>   Preference:     240
>   Input filter:   ACCEPT
>   Output filter:  REJECT
>   Routes:         0 imported, 0 exported, 0 preferred
>   Route change stats:     received   rejected   filtered    ignored   accepted
>     Import updates:              0          0          0          0          0
>     Import withdraws:            0          0        ---          0          0
>     Export updates:              0          0          0        ---          0
>     Export withdraws:            0        ---        ---        —          0
> 
> Nothing to say about this one, from what I have read it’s role is to feed the kernel protocol.
> 
> static1  Static   master   up     17:41:12
>   Preference:     200
>   Input filter:   ACCEPT
>   Output filter:  ACCEPT
>   Routes:         1 imported, 0 exported, 0 preferred
>   Route change stats:     received   rejected   filtered    ignored   accepted
>     Import updates:              1          0          0          0          1
>     Import withdraws:            0          0        ---          0          0
>     Export updates:              0          0          0        ---          0
>     Export withdraws:            0        ---        ---        ---          0
> 
> This one is annoying me and I think the issue is there, 1 imported but ignored, why ?
> 
> bgp1     BGP      master   up     17:41:13    Established
>   Preference:     100
>   Input filter:   ACCEPT
>   Output filter:  (unnamed)
>   Routes:         0 imported, 0 exported, 0 preferred
>   Route change stats:     received   rejected   filtered    ignored   accepted
>     Import updates:              0          0          0          0          0
>     Import withdraws:            0          0        ---          0          0
>     Export updates:              3          0          3        ---          0
>     Export withdraws:            0        ---        ---        ---          0
>   BGP state:          Established
>     Neighbor address: 10.10.2.1
>     Neighbor AS:      3000
>     Neighbor ID:      10.10.2.1
>     Neighbor caps:    refresh restart-aware AS4
>     Session:          internal multihop AS4
>     Source address:   10.10.1.1
>     Hold timer:       162/240
>     Keepalive timer:  53/80
> 
> I don’t understand why 3 routes are received because protocols direct1 and kernel1 should not export anything, and only one static route should be received via BGP from host2 ! Also the ouput filter is unamed, which I thinks is not good.
> 
> Below the host1 bird.conf.
> 
> As you can see I think I misunderstand some things, and I am a bit disappointed.
> 
> Cheers
> 
> 
> router id 10.10.1.1;
> protocol direct {
>         interface "*";  # Restrict network interfaces it works with
> }
> protocol kernel {
>         learn;                  # Learn all alien routes from the kernel
>         #persist;               # Don't remove routes on bird shutdown
>         scan time 20;           # Scan kernel routing table every 20 seconds
>         import all;             # Default is import all
>         export none;            # Default is export none
> }
> protocol device {
>         scan time 10;           # Scan interfaces every 10 seconds
> }
> protocol static static1 {
>         route 192.168.1.0/24 via 10.10.1.1;
>         export all;
> }
> protocol bgp {
>         multihop;
>         #gateway recursive;
>         import all;
>         export where proto = "static1";
>         local as 3000;
>         neighbor 10.10.2.1 as 3000;
>         #next hop self;
>         #rr client;
> }
> 
>> Cédric Lemarchand
> 
>> On 23 Feb 2017, at 17:10, Ondrej Zajicek <santiago at crfreenet.org> wrote:
>> 
>>> On Thu, Feb 23, 2017 at 04:42:50PM +0100, Cedric Lemarchand wrote:
>>> Yes, I am not sure to understand how plays theses options (and if I need it) in the bgp protocol and it they are related to my problem :
>>> 
>> 
>> 
>>> gateway recursive : means that if host2 advertise "route 192.168.2.0/24
>>> via 10.10.2.1;” to host1, host1 does a lookup in the kernel routing table
>>> and set the nexthop for 192.168.2.0/24 via the same IP as for host2 ?
>> 
>> Mainly yes, but:
>> 
>> 1) Not lookup in the kernel routing table, but in the BIRD table. By
>> default the same table as used by BGP protocol, but could be configured
>> to different one by 'igp table' option.
>> 
>> 2) It is not lookup for host2, but lookup for bgp_next_hop attribute, as
>> specified by host2, which is usually value of 'via'.
>> 
>>> next hop self : means that every route advertised by host2 will be routed to it self while keeping the “gateway recursive” logic ?
>> 
>> That means host2 always announces own IP address as bgp_next_hop instead
>> of one from 'via'.
>> 
>>> The output of show route all :
>> 
>> There are two issues:
>> 
>> 1) both hosts announce all routes (not only 192.168.xx but also 10.10.xx).
>> 
>> 2) routes from kernel1 protocol has lower preference (10), so routes
>> from BGP are preferred and you get circular lookups for 10.0.1.1, 10.10.2.1
>> 
>> You could change preference of kernel protocol to say 200 and you
>> could filter out unwanted routes in BGP export filter.
>> 
>> -- 
>> Elen sila lumenn' omentielvo
>> 
>> Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
>> OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net)
>> "To err is human -- to blame it on a computer is even more so."
> 
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