[dev] bug fix: ospf6d self orig MaxAge LSA

Santosh P K sapk at vmware.com
Wed Dec 4 11:54:46 EST 2019


Hello Yasu,
    You are right that your network will be back-holed until the old MAXAGE is flushed out from neighbors. MAXAGE self originated should be accepted for flushing out old instance from network faster and then generate the new version. By accepting maxaged self originated LSA we trigger event to refresh LSA as part of that we originate new LSA. With early return that is getting short circuited which is causing issue. 


With the same commit I saw the below code changes too. 

			/* Neighbor router sent recent age for LSA,
			 * Router could be restarted while current copy is
			 * MAXAGEd and not removed.*/
			if (OSPF6_LSA_IS_MAXAGE(old) &&
			    !OSPF6_LSA_IS_MAXAGE(new)) {

				if (is_debug)
					zlog_debug("%s: Current copy of LSA %s is MAXAGE, but new has recent Age.",
						   old->name,
					   __PRETTY_FUNCTION__);

				ospf6_lsa_purge(old);
				if (new->header->adv_router
						!= from->ospf6_if->area->
							ospf6->router_id)
					ospf6_flood(from, new);

				ospf6_install_lsa(new);
				return;
			}

I am not sure if this is right as if there is a MAXAGE copy in local database then we should not be accepting new instance of the same as router wishes to FLUSH it from the network. Not sure why this is done. Chirag who did this changes can help with some background. 

Thanks
Santosh P K 

´╗┐On 04/12/19, 5:05 PM, "dev on behalf of Yasuhiro Ohara" <dev-bounces at lists.frrouting.org on behalf of yasu at nttv6.jp> wrote:

    
    Hi,
    
    Today I fixed a bug in ospf6d.
    The bug seems to be introduced in the following commit.
    
    commit 76249532faadfb429f46dd94cf6bbc61d78b3f26
    Date:   Fri Jan 26 14:53:43 2018 -0800
    
        ospf6d: Handle Premature Aging of LSAs
    
    When ospf6d is restarting, self originated MaxAged LSAs
    may be floating around in the network, and the rebooting ospf6d
    is likely to receive them from the neighbor, probably with the
    higher LS-Seq-Num (which is more recent).
    The code introduced by the above commit in ospf6_flood.c:
    @@ -806,6 +818,17 @@
    was removing the more-recent self-originated MaxAged LSAs
    immediately in the receiving process of the LSA, prevent the
    LSAs from being installed in the local LSDB.
    The just rebooted ospf6d will have the lower LS-Seq-Num, so
    it cannot refresh the higher LS-Seq-Num version of the old LSA.
    So the ospf6d essentially couldn't advertise any information
    when the situation occured.
    
    The bug was significant: the LSAs that can't be updated
    in my network included the Router-LSA and the Intra-Area-Prefix-LSA,
    so the address in the loopback I/F was not advertised
    and the BGP session cannot be established at all.
    At some point, the MaxAged LSAs floating in the
    network may vanish (I don't know the reason why yet),
    and sometimes the problem doesn't occur.
    
    Commenting out the code by #if 0 immediately solved the problem:
    the self-originated MaxAged LSAs are installed in the local LSDB
    once, and then ospf6d refreshes it with the updated contents,
    and then floods. 
    
    I will make a pull-request later.
    
    ~/frr/ospf6d# git diff
    diff --git a/ospf6d/ospf6_flood.c b/ospf6d/ospf6_flood.c
    index 0828c2beb..67172dd4a 100644
    --- a/ospf6d/ospf6_flood.c
    +++ b/ospf6d/ospf6_flood.c
    @@ -842,6 +842,7 @@ void ospf6_receive_lsa(struct ospf6_neighbor *from,
                                    zlog_debug("Received is duplicated LSA");
                            SET_FLAG(new->flag, OSPF6_LSA_DUPLICATE);
                    }
    +#if 0
                    if (old->header->adv_router
                                == from->ospf6_if->area->ospf6->router_id
                        && OSPF6_LSA_IS_MAXAGE(new)) {
    @@ -854,6 +855,7 @@ void ospf6_receive_lsa(struct ospf6_neighbor *from,
                                            ismore_recent);
                            return;
                    }
    +#endif /*0*/
            }
     
            /* if no database copy or received is more recent */
    
    Best regards,
    Yasu
    
    
    
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