[j-nsp] OSPF Sham link question

Daniel Lete daniel.lete at heanet.ie
Thu Dec 6 10:04:03 EST 2007


Hello David,
Your comment below:
 > (NB: is it normal that the routes PE2 is learning from the m10 are 'Extern' ?)

may not be related at all with sham links or even with rfc2547/rfc4364. If you 
are injecting prefixes into OSPF (redistribute in Cisco or export in Juniper) 
in your CE, then those prefixes will appear as LSA Type-5 (external if you want).

Daniel



David Ball wrote:
>   Should have mentioned earlier (in case it's relevant), the reason
> for sham-link requirement is that there 'will' be a slow backup link
> between the cisco and the m10, but it'll be direct, so the cisco and
> m10 will think that's the better link (due to intra-area).  So, was
> hoping to use sham-link across T640s to bring things closer to 'par'
> and have those routes appear as intra-area and ultimately prefer the
> sham-link.
>   I was, but am no longer, explicitly exporting routes from BGP into
> OSPF on the PEs.  As requested, more configs and show cmd output
> included.  I appreciate the feedback so far by the way....thanks
> again.
> 
> m10's loopback is 172.16.0.3
> cisco's loopback is 172.16.0.4
> 
> Pertinent configs from PE1 (T640 facing Cisco):
> lo0 {
>     unit 800 {
>         description "sham-link testing";
>         family inet {
>             filter {
>                 input secure-router-shamlink-test;
>             }
>             address 172.16.0.2/32;
>         }
>     }
> }
> 
> ge-7/0/0 {  <---- int facing Cisco
>     unit 0 {
>         family inet {
>             address 172.16.2.1/30;
>         }
>     }
> }
> 
> sham-link-test {
>     instance-type vrf;
>     interface ge-7/0/0.0;
>     interface lo0.800;
>     vrf-target target:25983:800;
>     vrf-table-label;
>     protocols {
>         ospf {
>             sham-link local 172.16.0.2;
>             area 0.0.0.0 {
>                 sham-link-remote 172.16.0.1 metric 1;
>                 interface ge-7/0/0.0 {
>                     metric 1;
>                 }
>             }
>         }
>     }
> }
> 
> 
> Pertinent configs from PE2 (T640 facing M10):
> 
> lo0 {
>     unit 800 {
>         description "sham-link test";
>         family inet {
>             filter {
>                 input secure-router-shamlink-test;
>             }
>             address 172.16.0.1/32;
>         }
>     }
> }
> 
> ge-7/2/1 {      <--------facing m10
>     unit 0 {
>         family inet {
>             address 172.16.1.1/30;
>         }
>     }
> }
> 
> sham-link-test {
>     instance-type vrf;
>     interface ge-7/2/1.0;
>     interface lo0.800;
>     vrf-target target:25983:800;
>     vrf-table-label;
>     protocols {
>         ospf {
>             sham-link local 172.16.0.1;
>             area 0.0.0.0 {
>                 sham-link-remote 172.16.0.2 metric 1;
>                 interface ge-7/2/1.0 {
>                     metric 1;
>                 }
>             }
>         }
>     }
> }
> 
> OSPF neighbors as seen from PE1:
>> show ospf neighbor instance sham-link-test
>   Address         Interface             State      ID              Pri  Dead
> 172.16.2.2       ge-7/0/0.0             Full      172.16.0.4         1    36
> 
> OSPF neighbors as seen from PE2:
>> show ospf neighbor instance sham-link-test
> Address          Interface              State     ID               Pri  Dead
> 172.16.1.2       ge-7/2/1.0             Full      172.16.0.3       128    31
> 
> Proof that PE1 is learning PE2's loopback via BGP:
>> show route table sham-link-test
> 
> sham-link-test.inet.0: 9 destinations, 9 routes (9 active, 0 holddown, 0 hidden)
> + = Active Route, - = Last Active, * = Both
> 
> 172.16.0.1/32      *[BGP/170] 12:43:03, localpref 100, from 1.7.1.43
>                       AS path: I
>                     > to 1.7.2.18 via ge-0/2/0.0, label-switched-path
> NCP-LSP-00819-005-043
>                       to 1.7.2.1 via ge-0/0/0.0, label-switched-path
> NCP-LSP-00819-005-043
> 172.16.0.2/32      *[Direct/0] 20:29:55
>                     > via lo0.800
> 
> Proof that PE2 is learning PE1's loopback via BGP:
>> show route table sham-link-test
> 
> sham-link-test.inet.0: 9 destinations, 9 routes (9 active, 0 holddown, 0 hidden)
> + = Active Route, - = Last Active, * = Both
> 
> 172.16.0.1/32      *[Direct/0] 21:04:41
>                     > via lo0.800
> 172.16.0.2/32      *[BGP/170] 18:50:17, localpref 100, from 1.7.1.5
>                       AS path: I
>                     > to 1.7.2.17 via ge-0/2/0.0, label-switched-path
> NCP-LSP-00829-043-005
>                       to 1.7.2.5 via ge-0/0/0.0, label-switched-path
> NCP-LSP-00829-043-005
> 
> OSPF database according to PE1 (Cisco isn't sending much/anything...my
> current goal is for the Cisco to learn what the m10 sends, then I'll
> move on):
>> show ospf database instance sham-link-test
> 
>     OSPF link state database, Area 0.0.0.0
>  Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len
> Router  *172.16.0.2       172.16.0.2       0x80000037   876  0x22 0xfdff  36
> Router   172.16.0.4       172.16.0.4       0x80000029  1111  0x22 0xa757  36
> Network  172.16.2.2       172.16.0.4       0x80000022  1372  0x22 0x9a80  32
> 
> 
> OSPF database according to PE2:
>> show ospf database instance sham-link-test
> 
>     OSPF link state database, Area 0.0.0.0
>  Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len
> Router  *172.16.0.1       172.16.0.1       0x80000024  1912  0x22 0x1ef6  36
> Router   172.16.0.3       172.16.0.3       0x80000425   735  0x22 0xc475  48
> Network  172.16.1.2       172.16.0.3       0x8000002e   435  0x22 0x7b97  32
> OpaqArea 1.0.0.1          172.16.0.3       0x80000413  1335  0x22 0xaeea  28
>     OSPF AS SCOPE link state database
>  Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len
> Extern   172.16.16.0      172.16.0.3       0x80000034  1035  0x22 0xbf33  36
> Extern   192.168.101.0    172.16.0.3       0x80000036   135  0x22 0xe40a  36
> 
> (NB: is it normal that the routes PE2 is learning from the m10 are 'Extern' ?)
> 
> Here is Cisco's current routing table (learning nothing via OSPF):
> lab-2651#sho ip route
> Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
>        D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
>        N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
>        E1 - OSPF external type 1, E2 - OSPF external type 2
>        i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
>        ia - IS-IS inter area, * - candidate default, U - per-user static route
>        o - ODR, P - periodic downloaded static route
> 
> Gateway of last resort is not set
> 
> C    172.17.0.0/16 is directly connected, FastEthernet0/1
>      172.16.0.0/30 is subnetted, 1 subnets
> C       172.16.2.0 is directly connected, FastEthernet0/0
> C    208.98.239.0/24 is directly connected, FastEthernet0/1
> lab-2651#
> 
> 
> Here is M10's inet.0 routing table:
>> show route
> 
> inet.0: 10 destinations, 10 routes (10 active, 0 holddown, 0 hidden)
> Restart Complete
> + = Active Route, - = Last Active, * = Both
> 
> 0.0.0.0/0          *[Static/5] 5w4d 23:37:59
>                       Reject
> 172.16.0.3/32      *[Direct/0] 2w0d 19:06:21
>                     > via lo0.0
> 172.16.1.0/30      *[Direct/0] 21:05:30
>                     > via ge-0/1/0.0
> 172.16.1.2/32      *[Local/0] 21:05:30
>                       Local via ge-0/1/0.0
> 172.16.16.0/24     *[Static/5] 21:02:54
>                       Discard
> 192.168.8.0/24     *[Static/5] 5w4d 23:37:59
>                     > to 192.168.101.252 via fxp0.0
> 192.168.9.0/24     *[Static/5] 5w4d 23:37:59
>                     > to 192.168.101.252 via fxp0.0
> 192.168.101.0/24   *[Direct/0] 5w4d 23:37:59
>                     > via fxp0.0
> 192.168.101.33/32  *[Local/0] 5w4d 23:37:59
>                       Local via fxp0.0
> 224.0.0.5/32       *[OSPF/10] 5w4d 23:38:00, metric 1
>                       MultiRecv
> 
> 
> 
> On 05/12/2007, Peter E. Fry <pfry-lists at redsword.com> wrote:
>> ----- Original Message -----
>> From: Daniel Lete <daniel.lete at heanet.ie>
>>
>> [...]
>>> In relation to your sham-link. You need a loopback IP
>>> within your VRF to act as  source/destination of the sham
>>> link and these loopbacks are NOT to be announced  to your
>>> CE.
>>  I was going to make that point -- that is, I would not
>> expect to see:
>>
>>> O IA    172.16.0.3/32 [110/11] via 172.16.2.1, 04:31:29,
>> FastEthernet0/0
>>
>> ...(although I could be wrong -- I don't get many looks into
>> CPE).  Also, I'd expect the sham-link neighbor to show up on
>> the PE.  You can see them on Cisco PEs, for instance:
>>
>> CiscoPE#show ip ospf [process] neighbor
>>
>> Neighbor ID     Pri   State           Dead Time   Address
>>     Interface
>> [...]
>> [Remote ID IP]    0   FULL/  -           -        [Remote LB
>> IP]  OSPF_SLn
>> [...]
>> CiscoPE#
>>
>> ...so there's no confusion as to the state of the sham link.
>>  I don't have a Juniper L3 VPN PE or a Cisco CE handy.
>>
>> Peter E. Fry
>>
>>
>>
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