Advanced Networks Masters - Past Exam Questions (Routing)?

gocall01

Hi,

First time poster here.
I am currently doing an advanced networks maters but have very little experience with respect to this module of the course.
I'm looking for a few answers for some past exam questions, any help will be greatly appreciated.

So, to begin:

Question #1 (EIGRP).
A network administrator has been monitoring his company's redundant network links, all of which are lower capacity than the primary links and is concerned because the redundant links appear to be carrying user traffic. The routing protocol used in the network is EIGRP and it was configured by an external consultant.
Explain why the redundant links are carrying user traffic and what your response to the network administrator would be.

Question #2 (OSPF).
A network administrator using Wireshark has detected multicast traffic on Ethernet switched network and having searched employees' PCs for multiplayer networked games like Quake or Unreal Tournament has found nothing. OSPF is the routing protocol used on the network.
What advice could you give to the adminstrator?


Thanks in advance,
Regards,
Ger.

Dieg0M

1. EIGRP can do unequal load balancing between 2 links that have different metrics by tweaking the K values with the Variance command under the EIGRP process.
2. OSPF for IPv4 uses 224.0.0.5 and 224.0.0.6 multicast addresses. 224.0.0.5 is used for maintaining neighbor adjacency through Hello's and 224.0.0.6 is used for the DR in a multiaccess network segment to propagate LSA type 1 and 2's within the Area.

networker050184

Why don't you tell us what you think the answers are and we can help point you in the right direction.

gocall01

OK, I was hoping not to embarrass myself but with the hope of getting the answer, here goes...
I'll try question #1 for a start.

Question #1 (EIGRP).
A network administrator has been monitoring his company's redundant network links, all of which are lower capacity than the primary links and is concerned because the redundant links appear to be carrying user traffic. The routing protocol used in the network is EIGRP and it was configured by an external consultant.
Explain why the redundant links are carrying user traffic and what your response to the network administrator would be.

Dieg0M wrote: »

1. EIGRP can do unequal load balancing between 2 links that have different metrics by tweaking the K values with the Variance command under the EIGRP process.

Extrapolating from DiegoM's post:
I am assuming mutlicast addressing over all links from the host router and therefore is it that simple that all links including redundant links will carry traffic.
Would this traffic be "system" traffic rather than "user" traffic, or is it all the same?
With respect to "Unequal Load Balancing" within the EIGRP protocol this mean links of different kbps can operate together.
This load balancing can be proportional so if the 2 links have say 2/3, 1/3 capacity ratio then the traffic load is proportionally 2/3, 1/3.
This allows all links to a destination to be used to carry data without overloading the slower link or limiting the faster link.

Once the load balancing appears to be proportional there would be no recommendation to the network administrator.

OK?

networker050184

gocall01 wrote: »

I am assuming mutlicast addressing over all links from the host router and therefore is it that simple that all links including redundant links will carry traffic.

No, the multicasting done by EIGRP is link local only. It is not forwarded.

gocall01 wrote: »

Would this traffic be "system" traffic rather than "user" traffic, or is it all the same?

Not sure what you mean by 'system' traffic.

gocall01 wrote: »

With respect to "Unequal Load Balancing" within the EIGRP protocol this mean links of different kbps can operate together.
This load balancing can be proportional so if the 2 links have say 2/3, 1/3 capacity ratio then the traffic load is proportionally 2/3, 1/3.
This allows all links to a destination to be used to carry data without overloading the slower link or limiting the faster link.

Once the load balancing appears to be proportional there would be no recommendation to the network administrator.

OK?

Sounds about right.

gocall01

networker050184 wrote: »

No, the multicasting done by EIGRP is link local only. It is not forwarded.

OK, must follow up on this point.

networker050184 wrote: »

Not sure what you mean by 'system' traffic.

The packets (Hello, Ack, Update,Query, Reply) are sorta system info.
I now realise this not significant with respect to the actual question.

networker050184 wrote: »

Sounds about right.

This I presume answers the question pretty well.

gocall01

Going to give question 2 a go now.

Question #2 (OSPF).
A network administrator using Wireshark has detected multicast traffic on Ethernet switched network and having searched employees' PCs for multiplayer networked games like Quake or Unreal Tournament has found nothing. OSPF is the routing protocol used on the network.
What advice could you give to the adminstrator?

2. OSPF for IPv4 uses 224.0.0.5 and 224.0.0.6 multicast addresses. 224.0.0.5 is used for maintaining neighbor adjacency through Hello's and 224.0.0.6 is used for the DR in a multiaccess network segment to propagate LSA type 1 and 2's within the Area.

Extrapolating from DiegoM's post:
Network topogoly changes create LSAs which are multicast to all neighbours using 224.0.0.5 (all OSPF routers listen on this) and 224.0.0.6. (all DR & BDR routers listen on this).
Routers receiving this info forward it to all neighbours.
Packets are continually sent to confirm adjancencies.
Therefore, there will always be multicast traffic on a OSPF network...

Advice for the network administrator:
None, as this multicast traffic should be expected.
However, an investigation into whether there is a two-layer hierarchy and DR/BDR implementation in place would be advisable.
The DR/BDR setup would substantially reduce the workload on the network routers.

OK?

Dieg0M

There will not always be multicast traffic in an OSPF network. If OSPF is configured for an NBMA network, the peering will be done through unicast instead. Also, DR/BDR election is done automatically in non point-to-point and point-to-multipoint networks. There is no "implementation" required to configure these.

gocall01

Dieg0M wrote: »

There will not always be multicast traffic in an OSPF network. If OSPF is configured for an NBMA network, the peering will be done through unicast instead. Also, DR/BDR election is done automatically in non point-to-point and point-to-multipoint networks. There is no "implementation" required to configure these.

Thanks Dieg0M.

With respect to the original question, what is causing the detection of multicast traffic?
What advice could you give to the adminstrator?

networker050184

The advice I'd give is to make segments with only users and no need for adjacency passive interfaces. I'd assume that is what they are trying to get out of you with that question.

Dieg0M

Or just configure passive-interface on every port that peering isn't needed.

gocall01

Thanks to both of you for your help to date.
Much appreciated.