On Tue, Nov 06, 2007 at 06:26:47PM +0100, Tony Sarendal wrote:
> New version. Less duplication and a nice feature as bonus.
> With softreconfig in enabled the looped prefixes are accepted
> into the Adj-RIB-In.
>
> This means that I can tell if my neighbor AS is using
> a path via myself. Either I'm tired or that is cool.
>
> router-02# bgpctl show rib 192.168.0.0
> flags: * = Valid, > = Selected, I = via IBGP, A = Announced
> origin: i = IGP, e = EGP, ? = Incomplete
>
> flags destination gateway lpref med aspath origin
> *> 192.168.0.0/16 192.168.100.5 100 0 65100 i
> * 192.168.0.0/16 172.17.1.1 100 0 65200 65100 i
> * 192.168.0.0/16 172.17.1.5 100 0 65200 65200 65200
> 65200 65100 i
> router-02#
>
> I now kill the peering that 65200 has to 65100, removing their
> direct path to 192.168.0.0/16.
>
> router-02# bgpctl show rib 192.168.0.0
> flags: * = Valid, > = Selected, I = via IBGP, A = Announced
> origin: i = IGP, e = EGP, ? = Incomplete
>
> flags destination gateway lpref med aspath origin
> *> 192.168.0.0/16 192.168.100.5 100 0 65100 i
> router-02#
>
> Sweet, the looping issue is gone.
> Here is the bonus:
>
> router-02# bgpctl show rib neigh 172.17.1.5 in | grep 65300
> * 172.17.0.2/32 172.17.1.5 100 0 65200 65300 i
> * 192.168.0.0/16 172.17.1.5 100 0 65200 65300 65100 i
> * 192.168.100.4/30 172.17.1.5 100 0 65200 65300 i
> router-02#
>
> I now see the paths that the peer uses my network to access.
> Note that this depends a bit on remote implementation.
> I think this works agains a cisco router.
>
> /Tony
>
>
> Index: rde.c
> ===================================================================
> RCS file: /cvs/src/usr.sbin/bgpd/rde.c,v
> retrieving revision 1.228
> diff -u -r1.228 rde.c
> --- rde.c 16 Sep 2007 15:20:50 -0000 1.228
> +++ rde.c 6 Nov 2007 17:08:50 -0000
> @@ -919,12 +919,6 @@
> /* shift to NLRI information */
> p += 2 + attrpath_len;
>
> - /* aspath needs to be loop free nota bene this is not a hard error */
> - if (peer->conf.ebgp && !aspath_loopfree(asp->aspath, conf->as)) {
> - error = 0;
> - goto done;
> - }
> -
> /* parse nlri prefix */
> while (nlri_len > 0) {
> if ((pos = rde_update_get_prefix(p, nlri_len, &prefix,
> @@ -977,10 +971,18 @@
> if (fasp == NULL)
> fasp = asp;
>
> - rde_update_log("update", peer, &fasp->nexthop->exit_nexthop,
> - &prefix, prefixlen);
> - path_update(peer, fasp, &prefix, prefixlen, F_LOCAL);
> -
> + rde_update_log("update", peer,
> + &fasp->nexthop->exit_nexthop,&prefix,
> + prefixlen);
> + /* handle an update with loop as a withdraw */
> + if (peer->conf.ebgp && !aspath_loopfree(asp->aspath,
> + conf->as))
> + prefix_remove(peer, &prefix, prefixlen,
> + F_LOCAL);
> + else
> + path_update(peer, fasp, &prefix, prefixlen,
> + F_LOCAL);
> +
> /* free modified aspath */
> if (fasp != asp)
> path_put(fasp);
> @@ -1075,9 +1077,15 @@
>
> rde_update_log("update", peer,
> &asp->nexthop->exit_nexthop,
> - &prefix, prefixlen);
> - path_update(peer, fasp, &prefix, prefixlen,
> - F_LOCAL);
> + &prefix, prefixlen);
> + /* handle an update with loop as a withdraw */
> + if (peer->conf.ebgp &&
> + !aspath_loopfree(asp->aspath,conf->as))
> + prefix_remove(peer, &prefix,
> + prefixlen,F_LOCAL);
> + else
> + path_update(peer, fasp, &prefix,
> + prefixlen,F_LOCAL);
>
> /* free modified aspath */
> if (fasp != asp)
I looked a bit closer at this problem and the RFC mentions that pathes
with loops need to be inserted into the RIB and will be ignored in phase 2
of the decision process.
So this diff does just about that. It does not remove any prefix if there
is a loop but instead is ignoring them during the route decision process.
This seems to work for me but I'm currently unable to do larger tests.
--
:wq Claudio
Index: rde.c
===================================================================
RCS file: /cvs/src/usr.sbin/bgpd/rde.c,v
retrieving revision 1.228
diff -u -p -r1.228 rde.c
--- rde.c 16 Sep 2007 15:20:50 -0000 1.228
+++ rde.c 6 Nov 2007 18:27:42 -0000
@@ -920,10 +920,8 @@ rde_update_dispatch(struct imsg *imsg)
p += 2 + attrpath_len;
/* aspath needs to be loop free nota bene this is not a hard error */
- if (peer->conf.ebgp && !aspath_loopfree(asp->aspath, conf->as)) {
- error = 0;
- goto done;
- }
+ if (peer->conf.ebgp && !aspath_loopfree(asp->aspath, conf->as))
+ asp->flags |= F_ATTR_ASLOOP;
/* parse nlri prefix */
while (nlri_len > 0) {
Index: rde.h
===================================================================
RCS file: /cvs/src/usr.sbin/bgpd/rde.h,v
retrieving revision 1.100
diff -u -p -r1.100 rde.h
--- rde.h 1 Jun 2007 04:17:30 -0000 1.100
+++ rde.h 6 Nov 2007 19:17:56 -0000
@@ -154,6 +154,7 @@ LIST_HEAD(prefix_head, prefix);
#define F_ATTR_MP_REACH 0x00040
#define F_ATTR_MP_UNREACH 0x00080
#define F_ATTR_AS4BYTE_NEW 0x00100 /* NEW_ASPATH or NEW_AGGREGATOR
*/
+#define F_ATTR_ASLOOP 0x00200
#define F_PREFIX_ANNOUNCED 0x01000
#define F_NEXTHOP_REJECT 0x02000
#define F_NEXTHOP_BLACKHOLE 0x04000
Index: rde_decide.c
===================================================================
RCS file: /cvs/src/usr.sbin/bgpd/rde_decide.c,v
retrieving revision 1.48
diff -u -p -r1.48 rde_decide.c
--- rde_decide.c 11 May 2007 11:27:59 -0000 1.48
+++ rde_decide.c 12 Nov 2007 05:43:20 -0000
@@ -120,6 +120,12 @@ prefix_cmp(struct prefix *p1, struct pre
return (-1);
if (!(p2->flags & F_LOCAL))
return (1);
+
+ /* only loop free pathes are eligible */
+ if (p1->flags & F_ATTR_ASLOOP)
+ return (-1);
+ if (p2->flags & F_ATTR_ASLOOP)
+ return (1);
asp1 = p1->aspath;
asp2 = p2->aspath;
@@ -239,8 +245,8 @@ prefix_evaluate(struct prefix *p, struct
xp = LIST_FIRST(&pte->prefix_h);
if (xp == NULL || !(xp->flags & F_LOCAL) ||
- (xp->aspath->nexthop != NULL && xp->aspath->nexthop->state !=
- NEXTHOP_REACH))
+ (xp->flags & F_ATTR_ASLOOP) || (xp->aspath->nexthop != NULL &&
+ xp->aspath->nexthop->state != NEXTHOP_REACH))
/* xp is ineligible */
xp = NULL;
