EIGRP and PPP
gojericho0
Member Posts: 1,059 ■■■□□□□□□□
in CCNP
I have two routers directly connected with both Ethernet and Serial links. The serial links connecting Router D and Router C are using PPP encapsulation with a \30 mask.
The other Serial Link (S0/1) is using on RTC is connecting to another router RTB using HDLC encapsulation and a \30 mask
My routing protocol is EIGRP and it has been enabled on all interfaces. Here are the ip int configs on both routers
Router
Router C:
Both connected interfaces have become neighbors and routing information is being shared and added to the respected topologies. Here is the topology for Router C
My questions are
Why is PPP creating 32 bit masks for the serial interfaces?
Why does HDLC not do this as well since it establishes a point to point link?
Why is the physical serial interface of RTC (10.200.1.1) listed in the topology table?
Why is 10.200.1.1 have an FD that is Inaccessible, it is running EIGRP?
The other Serial Link (S0/1) is using on RTC is connecting to another router RTB using HDLC encapsulation and a \30 mask
My routing protocol is EIGRP and it has been enabled on all interfaces. Here are the ip int configs on both routers
Router
RTD#sh ip int brief Interface IP-Address OK? Method Status Link FastEthernet0/0 10.8.0.5 YES manual up up Serial0/0 10.200.1.2 YES NVRAM up up FastEthernet0/1 unassigned YES manual administratively down down Serial0/1 unassigned YES NVRAM administratively down down Serial0/2 unassigned YES NVRAM administratively down down Loopback0 10.10.10.10 YES NVRAM up up Loopback1 20.20.20.20 YES NVRAM up up
Router C:
RTC#sh ip int brief Interface IP-Address OK? Method Status Link FastEthernet0/0 10.8.0.4 YES manual up up Serial0/0 10.200.1.1 YES manual up up FastEthernet0/1 unassigned YES manual administratively down down Serial0/1 10.200.2.1 YES manual up up Loopback0 30.30.30.30 YES NVRAM up up
Both connected interfaces have become neighbors and routing information is being shared and added to the respected topologies. Here is the topology for Router C
RTC#sh ip eigrp top
IP-EIGRP Topology Table for AS(1)/ID(30.30.30.30)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
P 30.30.30.30/32, 1 successors, FD is 128256
via Connected, Loopback0
P 20.20.20.20/32, 1 successors, FD is 156160
via 10.8.0.5 (156160/128256), FastEthernet0/0
via 10.200.1.2 (2297856/128256), Serial0/0
P 10.10.10.10/32, 1 successors, FD is 156160
via 10.8.0.5 (156160/128256), FastEthernet0/0
via 10.200.1.2 (2297856/128256), Serial0/0
P 10.8.0.0/24, 1 successors, FD is 28160
via Connected, FastEthernet0/0
P 10.200.2.0/30, 1 successors, FD is 2169856
via Connected, Serial0/1
P 10.200.1.2/32, 1 successors, FD is 2169856
via Rconnected (2169856/0)
P 10.200.1.1/32, 0 successors, FD is Inaccessible
via 10.8.0.5 (2172416/2169856), FastEthernet0/0
via 10.200.1.2 (2681856/2169856), Serial0/0
P 10.200.1.0/30, 1 successors, FD is 2169856
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - reply Status, s - sia Status
via Connected, Serial0/0
My questions are
Why is PPP creating 32 bit masks for the serial interfaces?
Why does HDLC not do this as well since it establishes a point to point link?
Why is the physical serial interface of RTC (10.200.1.1) listed in the topology table?
Why is 10.200.1.1 have an FD that is Inaccessible, it is running EIGRP?
Comments
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gojericho0
Member Posts: 1,059 ■■■□□□□□□□
My questions are
Why is PPP creating 32 bit masks for the serial interfaces?
Why does HDLC not do this as well since it establishes a point to point link?
Why is the physical serial interface of RTC (10.200.1.1) listed in the topology table?
Why is 10.200.1.1 have an FD that is Inaccessible, it is running EIGRP?
Well I think I figured out my first question and am using this answer to derive theories for the other questions. Someone please correct me if I am wrong:
1) There is an IPCP option that allows PPP to auto-negotiate an IP for the other end of the link. If an IP is already assigned or this option is disabled, a NACK will be sent from the remote host. The local host will see this reply and put a host route in the routing table.
2) HDLC does not do this since it is not designed to have CPs
3) Since 10.200.1.1 is derived from the IPCP function of PPP and not EIGRP, EIGRP has doesn't recognize it and considers in inaccessible -
EdTheLad
Member Posts: 2,111 ■■■■□□□□□□
Great question,this is something i never noticed and could appear in the ccie lab.
This is a feature of PPP called "peer neighbor-route" , so if you want to stop ppp advertising the /32 addresses you must disbale this feature on the interface and then toggle the port.
router(config-if)#no peer neighbor-routeNetworking, sometimes i love it, mostly i hate it.Its all about the $$$$ -
gojericho0
Member Posts: 1,059 ■■■□□□□□□□
EdTheLad wrote:Great question,this is something i never noticed and could appear in the ccie lab.
This is a feature of PPP called "peer neighbor-route" , so if you want to stop ppp advertising the /32 addresses you must disbale this feature on the interface and then toggle the port.
router(config-if)#no peer neighbor-route
Thanks Ed,
I can see this would be useful in a dynamic environment like a lab, but in my opinion this seems way to aggressive of a feature to be enabled automatically especially since it happens on a leased line with both connections in the same subnet!