CCNP - ENTERPRISE - OSPF - Area Types - Not-So-Stubby-Area (Dude!*)

(*sorry, can't help it - I just keep hearing some surf dude trying to think up a clever name to describe these area types and not succeeding very well...) 


Not-So-Stubby-Area (NSSA) - special area type for when you end up adding a way out of the network via a Stub Area. For example you take over another company and you want to extend their RIPv2 network in to yours by making a router that was in your stub area an ASBR.

ISP~~~~(ASBR1) ----AREA0----(RouterB)---Area1-NSSA---(RouterA)~~~~New RIPv 2 Network

• In the (crude) example above, RouterA was within the stub area attached to RouterB. It now has a path to external networks attached to it.
• To Address the fact that RouterA is in a stub area, this area is configured to be a NSSA and in turn RouterA directs Type7 LSA packets to the ABR, in this case RouterB.
• RouterB in turn takes this Type7 LSA and converts it in to a Type5, External Link, LSA and propagates into Area0.

Configure a NSSA

1) On all the routers in the NSSA do:

RouterA(config)#router ospf 1

RouterA(config-router)#no area 1 stub

   *remove the stub configuration

RouterA(config-router)#area 1 nssa

2) On the new ASBR within the NSSA redistribute your required RIPv2 netrworks:

RouterA(config)#router ospf 1

RouterA(config-router)#redistribute rip subnets

3) On the NSSA ABR, which is RouterB in the example above, do:

RouterB(config)#router ospf 1

RouterB(config-router)#area 1 nssa default-information originate

  *This causes RouterB to generate a O* N2 default route of 0.0.0.0/0 and propagate in to the NSSA

CCNP - ENTERPRISE - OSPF - Area Types - Totally Stubby Area (Dude!)

Totally Stubby Area - Cisco Proprietary, reduces the Routing Table further.

• Blocks external Type5 LSA's, Summary Type3 LSA's, and ASBR Type4 LSA's
• Totally Stubby Area only recognises intra-area routes and the default route 0.0.0.0
• ABR's inject the default route in to the Totally Stubby Area
• Each area router picks the closest ABR as its DFG

Configure a Totally Stubby Area

1) Configure OSPF as usual

2) Define the area to be Totally Stubby, as a Stub on all routers in the area, using the cmd:

R4(config)#router ospf 1

R4(config-router)#area 4 stub

3) On the ABR configure Area 3 to be Totally Stubby:

R5(config)#router ospf 1

R5(config-router)#area 4 stub no-summary

On the ABR the Routing Table will not change.

On the Totally Stubby router the routing table should only see routes in it's area and a default route to the ABR.

CCNP - ENTERPRISE - OSPF - Area Types - Stub Area

Stub Area - Does not accept Type5 LSA's (External routes)

• Type5 LSA's replaced by a default route from the ABR
• All routers within the Stub area must be configured as a Stub Router

Configure a Stub Router:

R1(config)# router ospf 1

R1(config-router)#area 2 stub

  *Note the adjacency will fail until the neighbor plus the ABR is configured as a Stub as well

NOTE - On the ABR #sh ip route - will not change

On the Stub router, #sh ip route - routes from the ABR are replaced by a default route.

CCNP - ENTERPRISE - OSPF - LSA types

Link-state Advertisement Types are as follows:
 Type
 1 - Router LSA - Most common, used in an Area, lists a routers neighbor and it's cost
 2 - Network LSA - Generated by DR/BDR, advertises all routes with in an area - Does not cross the ABR
 3 - Summary LSA - ABR's generate these to summarise routes from a different area, sent between areas,    summarisation is manually configured.
4 - ASBR LSA - Sent FROM an ABR with the IP's of ASBR's in any OSPF areas. Routes in OSPF areas use these to locate the external network.
5 - External Link LSA - Advertises ASBR summary routes out, contains routes external to OSPF
7 - NSSA External LSA - Similar to Type5 LSA but generated by an ASBR in a Not-So-Stubby-Area, converted in to Type5 LSA's by the receiving ABR

CCNP - ENTERPRISE - Study Pointers - IPv6

IPv6

• FF00::/8 = Multicast prefix for all multicast traffic
• Link-LSA's and Intra-area LSA's are not used in OSPFv2 (Included in OSPFv3)
• R2(config-if)#ipv6 ospf cost 50 - this cmd sets the cost of a packet on this interface
• R2(config)#ipv6 unicast-routing - required when configuring a router for IPv4/IPv6 Dual Stack
• In a tunnel the header will look like - | ipv4 header | ipv6 header | ipv6 data |
• In OSPFv3 Type3 and Type9 LSA's carry all IPv6 Prefix info
• Local-Link LSA's aree flooded through the OSPF area
• IPv6 autoconfiguration allows a device to connect to a network without further config or the use of a DHCP server
• Enable a IPv6-to-IPv4 tunnel using: 

          R3(config)#interface tunnel0
          R3(config-if)#tunnel mode ipv6ip
               *apply this on both ends of the tunnel

CCNP - ENTERPRISE - Study Pointers - Multicast

Multicast:

Disadvantages of Multicast:

• Lack of congestion control results in increased network degradation as the volume of network traffic rises
• Best effort delivery - can lead to packet drops affecting VOIP/Video delivery
• Eavesdropping is a security issue due to the nature to the protocol

Further points:

• 224.0.1.1 = NTP protocol
• GLOP and Limited scope addresses are types of Multicast address
• RP-Announce msgs sent to 224.0.1.39
• RP-Discovery msgs  (group-to-RP mapping msgs) sent to 224.0.1.40

CCNP - ENTERPRISE - Study Pointers - BGP

BGP:

• When configuring eBGP peers between peers that are not directly connected you use the - 'R2(config-router)#neighbor 192.168.10.1 ebgp-multihop [hops]' - cmd on both peers.
• On an iBGP router that is a border router configure- 'R2(config-router)#neighbor 172.16.30.1 next-hop-self' -  to advertise the next hop as it's self to the rest of the iBGP peers
• Send the default route information to a specific peer - 'R2(config-router)#neighbor 172.16.30.1 default-originate'
• 3 well know mandatory BGP attributes - AS_PATH, NEXT_HOP, Origin

CCNP - ENTERPRISE - Study Pointers - Route Redistribution

Route Redistribution:

• EIGRP Summary route AD = 5
• Passive Interfaces - Updates are not sent or received through the interface
• The cmd R3(config-if)#ip help-address 10.2.2.2 - is applied in the inbound interface on the DFG for the host :
• i.e  HOST -------*(R3)>>>><<<<(R4)--------DHCP Server1
• *applied at this interface

• DHCP Allocation Mechanisms - Automatic, Dynamic, Manual

CCNP - ENTERPRISE - Study pointers - OSPF

My notes study notes for OSPF:

• When configuring a virtual link you specify the are to be traversed plus the Router I.D. of the end point.
•  e.g. - R1(config-router)#area 5 virtual link 3.3.3.3
•  Then on remote router: R3(config-router)#area 5 virtual-link 1.1.1.1

• When working on a Frame-relay environment you need to enter the network type cmd under the OSPF process:
• R2(config-router)#ip ospf network non-broadcast
• At the interface you need to set OSPF priority to prevent DR election on the routers that will not be a DR:
• R2(config-if)#ip ospf priority 0

• An INIT state can exist when a router ID has not been seen in a received Hello Packet
• A Stub area doesn't accept information from outside of the OSPF AS
• ABR's maintain a separate link-state database for each area they are attached to.

CCNP - ENTERPRISE -IPv6 - 6to4 tunnel addresses

When you create a 6to4 tunnel you need to apply suitable IPv6 addresses to the tunnel interfaces.

To do this you can take your IPv4 IP address which will be the source IP and convert it to an IPv6 address.

1) Using a Global address you know 2 things A) the high order bits always start 001 = 2000::/3 and generally end with 0001 in the first 16bits and B) a Global prefix is 48 bits long ( or /48). With this in mind  you know your first 16 bits, 0010 0000 0000 0001: X:X:X:X:X:X:X, so you are looking for the remaining 32 bits to form the address

2) Copy out into binary the IPv4 address of the physical interface the tunnel will be be associated with then convert it to hex, e.g.) 192.168.99.1
    1100 0000. 1010 1000. 0110 0011. 0000 0001
      c     0        a      8       6     3      0     1

3) Combine this with your first 16 bits and you have your Global IPv6 to apply to your tunnel interface
     2001:c0a8:6301::/48

Practise doing this quickly, again I've not taken the exam, but just like subnetting and Multicast MAC addresses it strikes me as an obvious exam question and an easy mark to pick up quickly leaving you time to work on the harder questions.