Showing posts from March 3, 2013

Simple Network Management Protocol(SNMP) Operations

SNMPv1 Protocol OperationsSNMP is a simple request/response protocol. The network-management system issues a request, and managed devices return responses. This behavior is implemented by using one of four protocol operations: Get, GetNext, Set, and Trap. The Get operation is used by the NMS to retrieve the value of one or more object instances from an agent. If the agent responding to the Get operation cannot provide values for all the object instances in a list, it does not provide any values. The GetNext operation is used by the NMS to retrieve the value of the next object instance in a table or a list within an agent. The Set operation is used by the NMS to set the values of object instances within an agent. The Trap operation is used by agents to asynchronously inform the NMS of a significant event.
SNMPv2 Protocol OperationsThe Get, GetNext, and Set operations used in SNMPv1 are exactly the same as those used in SNMPv2. However, SNMPv2 adds and enhances some protocol operations. …

IP Multicast VPN Routing and Forwarding and Multicast Domains

IP Multicast VPN Routing and Forwarding and Multicast Domains
Multicast VPN introduces multicast routing information to the VPN routing and forwarding table. When a PE router receives multicast data or control packets from a customer-edge (CE) router, forwarding is performed according to the information in the Multicast VRF (MVRF).

A set of Multicast VPN Routing and Forwarding instances that can send multicast traffic to each other constitutes a multicast domain. For example, the multicast domain for a customer that wanted to send certain types of multicast traffic to all global employees would consist of all CE routers associated with that enterprise.
Multicast Distribution Trees
Multicast VPN establishes a static default MDT for each multicast domain. The default MDT defines the path used by PE routers to send multicast data and control messages to every other PE router in the multicast domain.

Multicast VPN also supports the dynamic creation of MDTs for high-bandwi…

PPPoA architectures Deployment Methods

How the Service Destination is Reached In PPPoA architectures, the service destination can be reached in different ways. Some of the most commonly deployed methods are: Terminating PPP sessions at the service providerL2TP TunnelingUsing SSG In all three methods there is a fixed set of PVCs defined from the CPE to the DSLAM that is switched to a fixed set of PVCs on the aggregation router. The PVCs are mapped from the DSLAM to the aggregation router through an ATM cloud. The service destination can also be reached using other methods such PPPoA with SVCs, or Multiprotocol Label Switching/Virtual Private Network. These methods are beyond the scope of this document and will be discussed in separate papers. Terminating PPP at Aggregation The PPP sessions initiated by the subscriber are terminated at the service provider which authenticates users using either a local database on the router or through RADIUS servers. After the user is authenticated, IPCP negotiation takes place and the IP add…

IS-IS DIS Election

Election of the DIS On a LAN, one of the routers elects itself the DIS, based on interface priority (the default is 64). 
If all interface priorities are the same, the router with the highest subnetwork point of attachment (SNPA) is selected. 
The SNPA is the MAC address on a LAN, and the local data link connection identifier (DLCI) on a Frame Relay network. 
If the SNPA is a DLCI and is the same at both sides of a link, the router with the higher system ID becomes the DIS. 
Every IS-IS router interface is assigned both a L1 priority and a L2 priority in the range from 0 to 127.
The DIS election is preemptive (unlike OSPF). If a new router boots on the LAN with a higher interface priority, the new router becomes the DIS. It purges the old pseudonode LSP and floods a new set of LSPs.

G.709 OPTICAL TRANSPORT NETWORK - Optical Payload Unit (OPU)

The optical transport network (OTN) was created with the intention of combining the benefits of SONET/SDH technology with the bandwidth expansion capabilities offered by dense wavelength-division multiplexing (DWDM) technology.

In addition to further enhancing the support for operations, administration, maintenance and provisioning (OAM&P)
functions of SONET/SDH in DWDM networks, the purpose of the ITU G.709 standard (based on ITU G.872) is threefold.

First, it defines the optical transport hierarchy of the OTN; second, it defines the functionality of its overhead in support of multiwavelength optical networks; and third, it defines its frame structures, bit rates and formats for mapping client signals.

Optical Payload Unit (OPU)In order to begin describing the OTN as defined by the ITU G.709 standard, we must first enumerate its critical elements, their termination points, and the way they relate to one another in terms of hierarchy and fun…

MPLS TE Policy-based Tunnel Selection(PBTS)


Advantages and Disadvantages of PPPoA Architecture

PPP over ATM adaptation layer 5 (AAL5) (RFC 2364) uses AAL5 as the framed protocol, which supports both PVC and SVC. PPPoA was primarily implemented as part of ADSL. It relies on RFC1483, operating in either Logical Link Control-Subnetwork Access Protocol (LLC-SNAP) or VC-Mux mode. A customer premises equipment (CPE) device encapsulates the PPP session based on this RFC for transport across the ADSL loop and the digital subscriber line access multiplexer (DSLAM).

Advantages and Disadvantages of PPPoA Architecture

PPPoA architecture inherits most of the advantages of PPP used in the Dial model. Some of the key points are listed below.

• Advantages

- Per session authentication based on Password Authentication Protocol (PAP) or Challenge Handshake Authentication Protocol (CHAP). This is the greatest advantage of PPPoA as authentication overcomes the security hole in a bridging architecture.

- Per session accounting is possible, which allows the service provider to charge the subscriber …

MPLS Traffic Engineering Components

Traffic Engineering Components
• Information distribution
• Path selection/calculation
• Path setup
• Trunk admission control
• Forwarding traffic on to tunnel
• Path maintenance

Carrier supporting carrier (CSC) feature using the IP Solution Center (ISC) provisioning process

To configure the CSC network to exchange routes and carry labels between the backbone carrier provider edge (CSC-PE) routers and the customer carrier customer edge (CSC-CE) routers, use Label Distribution Protocol (LDP) to carry the labels and an Internal Gateway Protocol (IGP) to carry the routes.


A routing protocol is required between the CSC-PE and CSC-CE routers that connect the backbone carrier to the customer carrier. The routing protocol enables the customer carrier to exchange IGP routing information with the backbone carrier. RIP, OSPF, or static routing as the routing protocol can be selected.

Label distribution protocol (LDP) is required between the CSC-PE and CSC-CE routers that connect the backbone carrier to the customer carrier. LDP is also required on the CSC-PE to CSC-CE interface for VPN routing/forwarding (VRF).

• IPv4 BGP Label Distribution

BGP takes the place of an IGP and LDP in a VPN forwarding/routing instance (VRF) table. You can use BGP to distribut…

IS-IS Designated Intermediate System (DIS) Tasks

On broadcast multi-access networks, a single router is elected as the DIS. There is no backup DIS elected. The DIS is the router that creates the pseudonode and acts on behalf of the pseudonode.

Two major tasks are performed by the DIS:

1. Creating and updating pseudonode LSP for reporting links to all systems on the broadcast subnetwork. See the Pseudenode LSP section for more information.

2. Flooding LSPs over the LAN.

Flooding over the LAN means that the DIS sends periodic complete sequence number protocol data units (CSNPs) (default setting of 10 seconds) summarizing the following information:

Sequence Number
Remaining Lifetime

The DIS is responsible for flooding. It creates and floods a new pseudonode LSP for each routing level in which it is participating (Level 1 or Level 2) and for each LAN to which it is connected. A router can be the DIS for all connected LANs or a subset of connected LANs, depending on the IS-IS priority or the Layer 2 address. The DIS will …

What does r RIB-Failure mean in the show ip bgp command output?

When BGP tries to install the best path prefix into Routing Information Base (RIB) (for example, the IP Routing table), RIB might reject the BGP route due to any of these reasons:

1. Route with better administrative distance already present in IGP. For example, if a static route already exists in IP Routing table.

2. Memory failure.

3. The number of routes in VPN routing/forwarding (VRF) exceeds the route-limit configured under the VRF instance.

In such cases, the prefixes that are rejected for these reasons are identified by r RIB Failure in the show ip bgp command output and are not advertised to the peers. This feature was first made available in Cisco IOS Software Release 12.2(08.05)T.

Qnet symlink manager (QSM)

Qnet is a QNX Neutrino protocol for communication between processes residing on different nodes. It enables IPC to work across nodes. For example, LWM uses Qnet transparently to enable inter-node communication.

The use of a symbolic link (symlink) enables location transparency to the Qnet protocol. When a process needs to communicate with another process, it uses the symlink associated with the service and does not need to know where the service is located. A server process registers with Qnet symlink manager (QSM) and publishes its service using symlink.

NTP Version 4

According to the NTP Version 4 Release Notes found in release.htm, the new features of version four (as compared to version three) are:

Use of floating-point arithmetic instead of fixed-point arithmetic.
Redesigned clock discipline algorithm that improves accuracy, handling of network jitter, and polling intervals.
Support for the nanokernel kernel implementation that provides nanosecond precision as well as improved algorithms.
Public-Key cryptography known as autokey that avoids having common secret keys.
Automatic server discovery (manycast mode)
Fast synchronization at startup and after network failures (burst mode)
New and revised drivers for reference clocks
Support for new platforms and operating systems

Packet Tracer Simulation Lab Layer 2 Switching

Packet Tracer Simulation Lab Layer3 Routing