Friday, February 26, 2010

Basics Of IS-IS

IS-IS(ISO 10589) is Integrated System to Integrated System which was initially designed by DEC for OSI then tuned to work for TCP/IP protocol by the IETF in RFC 1195. In other words we can say a robust protocol which now supports the both ip as well as CLNP applications. It is a link state routing protocol and uses the same DIJKSTRA algorithm as being used by OSPF (Open Shortest Path First) to calculate the path cost.
IS-IS maintains three types of tables:-
1. Neighbor Table
2. Routing Table
3. Topology Table

Address Format Used By IS-IS
OSI uses connectionless Network Service aka CLNS which is equivalent to IP in TCP/IP. CLNP assigning addresses to a router called Network Service Access Point(NSAP) addresses or Network Entity Title(NET) addresses. IS-IS uses a one address per node. Net addresses can be up to 20 bytes in length. CISCO implementation of NET address tells about area, system id and NSAP selector.

Types Of Router
1. Level 1 (L1) – It maintains the topology database of its own area.
2. Level 2 router consider as backbone router.
3. Level 1-2 routers are interfaces between the Level 1 and Level 2.

The main advantage of using IS-IS because of it’s TLV (Type/Length/Value) which makes it unique from legacy OSPF. It is a hearsay that support of IPv6 in OSPF requires lot of modification from it’s root but the presence of TLV in IS-IS helped it to support IPv6 with no more changes.

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Wednesday, February 24, 2010

Which Protocol Is Used As IGP For IPv6?

Selection of IGP for IPv6 is agnostic for dual stack scenarios in mpls vpn backbones or ip backbones. Everyone is having a question that we are using OSPF as IGP for IPv4, which protocol is used as IGP for IPv6. No one is actually putting light which one is best for IPv6 where in OSPF already deployed for IPv4 in most of the cases. During reading RFC 4029 “Selection and Analysis For Introducing IPv6 into SP Networks”, I found section 4.3.1 of IGP which is explicitly defining the protocols require for IGP in IPv6 deployments. According to RFC OSPFv3,IS-IS is used but CISCO is also providing IPv6 support for EIGRP and RIPng is clearly renounce. If we are using the same protocol for both IPv6 as well as for IPv6, it may lead to lot of the problems in case of instability of links because every time protocol has to calculate the path for each and every link. But in case of different protocols for IPv4 and IPv6, the problem in one protocol may not affect another but this requires lot of CPU as well as memory.

Possible combinations are as follows:
1. OSPFv2 for IPv4, IS-IS for IPv6 (only)
2. OSPFv2 for IPv4, OSPFv3 for IPv6
3. IS-IS for IPv4, OSPFv3 for IPv6
4. S-IS for both IPv4 and IPv6
When IS-IS is used for both IPv4 as well as for IPv6, the IPv6/IPv6 topologies must be convex, unless multiple-topology IS-IS extensions have been implemented.

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Thursday, February 18, 2010

CCNA, CCNP, CCIE - Service Provider Operation Track

Cisco Announces New Service Provider Operations Track

Built on the growing demand for dedicated professionals who can manage, maintain and troubleshoot complex service provider IP NGN core network infrastructures, Cisco is introducing a new Service Provider (SP) Operations track. This new track is focused on developing associate, professional and expert-level capabilities to operate large, complex SP networks. These new, first of their kind certifications are designed specifically for Cisco Service Provider Customers, Partners and Cisco Networking Engineers.

Over the coming months Cisco will release new CCIE, CCNP, and CCNA SP Operations courses and exams. In addition, the written exam topics for the CCIE SP Operations certification are now available on the Cisco Learning Network. The CCIE SP Operations written exam is scheduled for release in the second quarter of 2010.
For more click here

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Wednesday, February 17, 2010

Spanning Tree Problems In Data Centres

Really a good conversation held with Terry Slattery about Spanning Layer 2 Between Data Centres and he has posted all about the design consideration in his recent post with the solution suggested. The outcome of the discussion consequences with Overlay Transport Virtualization and TRILL.

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Monday, February 15, 2010

Overlay Transport Virtualization (OTV)

Every organisation is in the race of expanding the network infrastructure with high availability of applications because of the rising demand of resources. Rising demand of high availability gives the birth to geographically dispersed data centers.

Maintain high availability, resiliency and scalability is one of the challenge during designing geographically dispersed data centers. To accomplish this network designers always look for layer 1, layer 2, layer 3 connectivity between the data centers. Layer 1 connectivity provides a dedicated fiber from one data center to another data center but the solution is only possible if both the locations are in same metro otherwise cost is one of the major constraint in case of geographically dispersed locations. Layer 2 connectivity is also one of the highly deployed solutions in case when the customers use storage connectivity over FCIP (Fiber Channel Over IP). Layer 2 connectivity can be accomplished by EoMPLS or L2VPN. The last one is Layer 3 solution which could purely be based on IP or MPLS cloud.

What does customer demand?
A customer always looks for economical, preeminent and optimizes solution. This is the responsibility of network consultant, designer or architect to provide the best solution according to the requirement. But in new era of technology customers are highly qualified and know what the solution available in market is. They always look for the layer 2 solution aka l2 which means to extend the lan (logical area network) to the remote data centre. This solution works fine in case of single location. But as the location grows; demand will change to extend the LAN to other locations consequence Virtual Private LAN Services (VPLS) need to be provisioned which has its own limitations.

Current Problems with Existing Technologies
1. Data Centres need to share the problems of originating in another data centers consequence downtime increases. This is because of same broadcast domain.
2. Not able to utilize the links properly w.r.t. to the devices. (VSS – Virtual Switching System has solved the problem)
3. VLAN and Mac-Address scalability.
4. Multicast
5. Convergence time.

To overcome all the existing problems Cisco has finally come up with new solution i.e. Overlay Transport Virtualization (OTV).

What is Overlay Transport Virtualization (OTV)?
OTV is “Mac in IP Technique” which uses encapsulation not the legacy tunnelling. Customer can forward the traffic on any transport medium which carries the ip packets. The mechanism is same like of proxy arp where in IP next hop will become the proxy for all the destination mac addresses. MAC address mappings are advertised by the control protocol which restricts the unknown flooding in the remote locations and logically bind all the locations in full mesh to utilize the network and resources its best without hampering another.

This feature is only available in Nexus 7000

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Thursday, February 11, 2010

IP Prefix-List

IP Prefix-list was always whirlwind to me. Every time I was stuck up with ge (greater than equal) or le (less than equal) keywords. So I finally made a mind to write up a strong posting on it, so that one can understand the concept from root and able to implement in network with full understanding. In posted tutorial I tried to explain the basic functionality of ip prefix-list, sequence numbers along with optional parameters ge and le.
Click here to read the full tutorial of IP Prefix-list.

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Saturday, February 6, 2010

Innovations can never be stopped

Innovations can never be stopped. I would like to share link of amazing clock which was being share by one of my friend.

The lines of the clock is given below:-

1st Line is Second's
2nd Line is Minute's
3rd Line is Hour's
4th Line is the Day of the week
5th Line is today's Date
6th Line is the Month
7th Line is Year
Click here to see the clock

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Monday, February 1, 2010


The network is performing well, unfortunately we received a call that the few of the directly connected to each other are not working and the links attached to the switches were also not working. After logging on to the switches, we saw a weird error message "%ETHCNTR-3-LOOP_BACK_DETECTED: Keepalive packet loop-back detected on FastEthernet0/1". Fa0/1 was uplink to another switch and the port state was showing error disabled. The switch port goes in error disable mode if it detects any error situation on the port. The port is shut down and need to enable manually or automatically if configured. By default, all the cisco switches and routers send loopback frames (ethertype 0x9000) with SA=DA=It’s own mac-address. If the Keepalive packet is received on the same port it was sent from, then a loop exists which even cannot be detected by spanning tree protocol. This is likely the same as of split horizon technique in layer three devices. The problem most likely arises because of unmanaged switches or hubs connected to the switches.
To overcome the problem, we need to add “no keepalive” command under interface which prevents the port from being disabled. This issue is documented in Cisco bug ID CSCea46385.

Disable "no errdisable detect cause loopback" command is another way to handle the problem. By doing this when the switch detects the error disable message of loopback, it will not take any action.

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