From: Joseph Saad (joseph.samir.saad@gmail.com)
Date: Sat Nov 10 2007 - 16:32:19 ART
Here's an elaboration on the issue.
R1
R6 (A1) (A0) R5.
R4
R1, R4 and R6 shares the same VLAN and is in area 1.
R1, R4 and R5 are on a Hub-n-spoke with R5 as the hub and is in area 0
R6 is the ASBR (where I am doing redistribution of static subnets).
Rack1R6(config-router)#do sh runn | s ip route|router ospf
router ospf 1
router-id 150.1.6.6
log-adjacency-changes
area 1 nssa
redistribute static subnets
network 150.1.6.6 0.0.0.0 area 1
network 155.1.146.6 0.0.0.0 area 1
ip route 160.1.6.0 255.255.255.0 Null0
The first ABR
Rack1R1#sh runn | s router ospf 1|ip route
router ospf 1
router-id 150.1.100.100
log-adjacency-changes
area 1 nssa
network 150.1.1.1 0.0.0.0 area 1
network 155.1.0.1 0.0.0.0 area 0
network 155.1.146.1 0.0.0.0 area 1
Rack1R1#sh ip route ospf
160.1.0.0/24 is subnetted, 1 subnets
O N2 160.1.6.0 [110/20] via 155.1.146.6, 01:04:19, FastEthernet0/0
150.1.0.0/16 is variably subnetted, 4 subnets, 2 masks
O 150.1.6.6/32 [110/2] via 155.1.146.6, 01:04:19, FastEthernet0/0
O 150.1.5.5/32 [110/65] via 155.1.0.5, 01:05:14, Serial1/0
O 150.1.4.4/32 [110/2] via 155.1.146.4, 01:04:19, FastEthernet0/0
>> "Note that the route to 160.1.6.0 shows as N2"
Rack1R1#sh ip ospf database | b Type-7
Type-7 AS External Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Tag
160.1.6.0 150.1.6.6 11 0x80000004 0x005C48 0
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
160.1.6.0 150.1.100.100 2037 0x80000002 0x002AC9 0
>> This shows that Router 1 is doing the translation and is
originating the Type-5 LSA in the OSPF domain (except Stub and NSSA
areas).
On the other ABR (R4)
Rack1R4#sh ip route ospf
160.1.0.0/24 is subnetted, 1 subnets
O E2 160.1.6.0 [110/20] via 155.1.146.6, 01:09:32, Ethernet0/1
150.1.0.0/16 is variably subnetted, 4 subnets, 2 masks
O 150.1.6.6/32 [110/11] via 155.1.146.6, 01:09:39, Ethernet0/1
O 150.1.5.5/32 [110/65] via 155.1.0.5, 01:10:23, Serial1/0
O 150.1.1.1/32 [110/11] via 155.1.146.1, 01:09:39, Ethernet0/1
>> "Note that the route to 160.1.6.0 shows as E2"
Rack1R4#sh ip ospf data | b Type-7
Type-7 AS External Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Tag
160.1.6.0 150.1.6.6 197 0x80000004 0x005C48 0
Type-5 AS External Link States
Link ID ADV Router Age Seq# Checksum Tag
160.1.6.0 150.1.100.100 180 0x80000003 0x0028CA 0
My questions are:
1) Why R1 is showing the route as N2 for 160.1.6.0?
2)isn't Type-5 preferred over Type-7?
I would have expeceted to see R1 to have this route as E2 (i.e. similar to R4).
Thanks,
Joseph.
On Nov 10, 2007 11:15 PM, Joseph Saad <joseph.samir.saad@gmail.com> wrote:
> Hi Shiran,
>
> I am referring to IE technology Lab "NSSA Area type 7to5 LSA
> Translator Election".
>
> Regarding your Answer:
>
> When you use a NSSA not so stubby area then the ASBR will generate N2
> for external into the area.
>
> >> "I am OK with that"
>
> E2 is for external routes and will be generated by ASBR.
>
> >> "I am OK with that for Normal Areas".
>
> in a router that have under his process an Area type NSSA will convert
> the Type 7 LSA to Type 5 when going from NSSA to the Backbone Area.
>
> >> "True, but what if we have multiple ABR such as this particular
> technology lab".
>
> there are no election for ABR or ASBR, if your router have under his
> process more then one area then he is ABR, if he have redistribution
> (or originating a default route) then he is ASBR.
>
> >> "True, but if you have multiple ABR's for the NSSA, one of them
> (i.e. with the highest router-id) is elected for translating the type
> 7 into type 5 LSA".
>
> Joseph.
>
>
>
>
> On Nov 10, 2007 11:00 PM, shiran guez <shiranp3@gmail.com> wrote:
> > when you use a NSSA not so stubby area then the ASBR will generate N2 for
> > external into the area.
> >
> > E2 is for external routes and will be generated by ASBR.
> >
> > in a router that have under his process an Area type NSSA will convert the
> > Type 7 LSA to Type 5 when going from NSSA to the Backbone Area.
> >
> > there are no election for ABR or ASBR, if your router have under his process
> > more then one area then he is ABR, if he have redistribution (or originating
> > a default route) then he is ASBR.
> >
> >
> >
> >
> >
> > On Nov 10, 2007 8:45 PM, Joseph Saad <joseph.samir.saad@gmail.com> wrote:
> >
> > >
> > >
> > >
> > > When I have 2 ABR's for an NSSA. The elected Type 7 to Type 5 LSA
> > > translator shows the route in the routing table as N2 while the other
> > > ABR shows it as E2 route.
> > >
> > > I can understand why the non-elected ABR shows the route as E2
> > > (because it receives both type 7 LSA and type 5 LSA and type 5 LSA
> > > will be preferred).
> > >
> > > What I can't understand is why the elected router shows the route as
> > > N2 though it is the one which originated the type 5 LSA and already
> > > has the type 7 LSA in its database.
> > >
> > > Can someone shed some light on why such behavior?
> > >
> > > _______________________________________________________________________
> > > Subscription information may be found at:
> > > http://www.groupstudy.com/list/CCIELab.html
> > >
> >
> >
> >
> > --
> > Shiran Guez
> > MCSE CCNP NCE1
> > http://cciep3.blogspot.com
> > http://www.linkedin.com/in/cciep3
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