Shahed Israr

Shahed Israr is a Network Engineer specializing in GPON, FTTH, and telecom access network technologies. With hands-on experience in Huawei OLT and ONT configuration, U2000 NMS deployment, iMaster NCE-FAN Lite management systems, firmware upgrades, and advanced network troubleshooting, he helps Internet Service Providers (ISPs) and network professionals deploy, manage, and optimize fiber optic networks efficiently. Through GPON Solution, he shares practical technical guides, real-world solutions, and professional knowledge to support engineers working in modern GPON infrastructure.

DMVPN Configuration With mGRE and NHRP

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DMVPN Configuration:

DMVPN stands for Dynamic Multipoint VPN and it is an effective solution for dynamic secure overlay networks. In short, DMVPN Configuration is combination of the following technologies: [boxads]

1) Multipoint GRE (mGRE)
2) Next-Hop Resolution Protocol (NHRP)
4) Dynamic Routing Protocol (EIGRP, RIP, OSPF, BGP)
3) Dynamic IPsec encryption
5) Cisco Express Forwarding (CEF)

Assuming that reader has a general understanding of what DMVPN is and a solid understanding of IPsec/CEF, we are going to describe the role and function of each component in details. In this post we are going to illustrate two major phases of DMVPN evolution:

1) Phase 1 – Hub and Spoke (mGRE hub, p2p GRE spokes)
2) Phase 2 – Hub and Spoke with Spoke-to-Spoke tunnels (mGRE everywhere)

As for DMVPN Phase 3 – “Scalable Infrastructure”, a separate post is required to cover the subject. This is due to the significant changes made to NHRP resolution logic (NHRP redirects and shortcuts), which are better being illustrated when a reader has good understanding of first two phases. However, some hints about Phase 3 will be also provided in this post.

You may follow bellow professor jaya chandran DMVPN configuration video tutorial, for learning better.

[bodylink]

Multipoint GRE:

Let us start with the most basic building component of DMVPN Configuration – multipoint GRE tunnel. Classic GRE tunnel is point-to-point, but mGRE generalizes this idea by allowing a tunnel to have “multiple” destinations.

DMVPN point-to-point gre tunnels
DMVPN point-to-point gre tunnels

This may seem natural if the tunnel destination address is multicast (e.g. 239.1.1.1). The tunnel could be used to effectively distribute the same information (e.g. video stream) to multiple destinations on top of a multicast-enabled network. Actually, this is how mGRE is used for Multicast VPN implementation in Cisco IOS. However, if tunnel endpoints need to exchange unicast packets, special “glue” is needed to map tunnel IP addresses to “physical” or “real” IP addresses, used by endpoint routers. As we’ll see later, this glue is called NHRP.

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BGP Attributes Categories

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BGP Attributes Categories

BGP Attributes Categories are 1) WELL-KNOWN, MANDATORY , 2) WELL-KNOWN, DISCRETIONARY, 3) OPTIONAL, TRANSITIVE, 4) OPTIONAL, NON-TRANSITIVE. details are: [boxads]

BGP Attributes Categories
BGP Attributes Categories

WELL-KNOWN, MANDATORY

AS-path: A list of the Autonomous Systems (AS) numbers that a route passes through to reach the destination. As the update passes through an AS the AS number is inserted at the beginning of the list. The AS-path attribute has a reverse-order list of AS passed through to get to the destination.

Next-hop: The next-hop address that is used to reach the destination.

Origin: Indicates how BGP learned a particular route. There are three possible types — IGP (route is internal to the AS), EGP (learned via EBGP), or Incomplete (origin unknown or learned in a different way).

WELL-KNOWN, DISCRETIONARY

Local Preference: Defines the preferred exit point from the local AS for a specific route.

Atomic Aggregate: Set if a router advertises an aggregate causes path attribute information to be lost.

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BGP Routing Protocol Overview

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BGP Routing Protocol Overview

Hi ! Today i will discuss about BGP Routing Protocol Overview. BGP is an Border gateway protocol, BGP mainly use for connect between different networks. It is the protocol used between Internet service providers (ISPs) and also can be used between an Enterprise and an ISP. BGP was built for reliability, scalability, and control. [boxads]

  • BGP stands for Border Gateway Protocol. Routers running BGP are termed BGP speakers.
  • BGP uses the concept of autonomous systems (AS). An autonomous system is a group of networks under a common administration. The Internet Assigned Numbers Authority (IANA) assigns AS numbers: 1 to 64511 are public AS numbers and 64512 to 65535 are private AS numbers.
  • Autonomous systems run Interior Gateway Protocols (IGP) within the system. They run an Exterior Gateway Protocol (EGP) between them. BGP version 4 is the only EGP currently in use.
  • Routing between autonomous systems is called interdomain routing.
  • The administrative distance for EBGP routes is 20. The administrative distance for IBGP routes is 200.
  • BGP neighbors are called peers and must be statically configured.
  • BGP uses TCP port 179. BGP peers exchange incremental, triggered route updates and periodic keepalives.
  • Routers can run only one instance of BGP at a time.
  • BGP is a path-vector protocol. Its route to a network consists of a list of autonomous systems on the path to that network.
  • BGP’s loop prevention mechanism is an autonomous system number. When an update about a network leaves an autonomous system, that autonomous system’s number is prepended to the list of autonomous systems that have handled that update. When an autonomous system receives an update, it examines the autonomous system list. If it finds its own autonomous system number in that list, the update is discarded.

BGP Databases

BGP uses three databases. The first two listed are BGP-specific; the third is shared by all routing processes on the router:

  • Neighbor database: A list of all configured BGP neighbors. To view it, use the show ip bgp summary command.
  • BGP database, or RIB (Routing Information Base): A list of networks known by BGP, along with their paths and attributes. To view it, use the show ip bgp command.
  • Routing table: A list of the paths to each network used by the router, and the next hop for each network. To view it, use the show ip route command.

BGP Message Types

BGP has four types of messages:

  • 1) Open: After a neighbor is configured, BGP sends an open message to try to establish peering with that neighbor. Includes information such as autonomous system number, router ID, and hold time.
  • 2) Update: Message used to transfer routing information between peers. Includes new routes, withdrawn routes, and path attributes.
  • 3) Notification: When a problem occurs that causes a router to end the BGP peering session, a notification message is sent to the BGP neighbor and the connection is closed.
  • 4) Keepalive: BGP peers exchange keepalive messages every 60 seconds by default. These keep the peering session active.
  • ROUTE-REFRESH: An optional message (negotiated during capability advertisement) that is sent to request dynamic BGP route updates from the Adj-RIB-Out table of a remote BGP speaker

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OSPF Load Balancing Example

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OSPF Load Balancing:

[boxads] Today I will show how to configure OSPF load balancing, If we follow bellow example we see a client is connected through two WAN connections with two broadband routers that both are use for Internet routing. We will enable and disable OSPF load balancing packets that are sourcing from the HOST to the WEB SERVER.   Following the diagram:

OSPF Load Balancing Tutorial
OSPF Load Balancing Tutorial

Now lets go our OSPF Load Balancing Configuration part………..

Router R1:

R1#
R1#conf t
R1(config)#ip cef
R1(config)#int loopback 0
R1(config-if)#ip address 1.1.1.1 255.255.255.255
R1(config-if)#ip ospf network point-to-point
R1(config-if)#exit

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NAT PAT Configuration Packet Tracer

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NAT PAT Configuration Packet Tracer

Today i will discuss how to configure NAT PAT Configuration Packet Tracer simulator. Network address translation (NAT) is the process of modifying IP address information in IP packet headers while in transit across a traffic routing device. [boxads]

There are two different types of NAT:

 

  • NAT
    • Static NAT: The simplest type of NAT provides a one-to-one translation of IP addresses. It is often also referred to as one-to-one NAT. In this type of NAT only the IP addresses, IP header checksum and any higher level checksums that include the IP address need to be changed. The rest of the packet can be left untouched (at least for basic TCP/UDP functionality, some higher level protocols may need further translation). Basic NATs can be used when there is a requirement to interconnect two IP networks with incompatible addressing. With static NAT, translations exist in the NAT translation table as soon as you configure static NAT command(s), and they remain in the translation table until you delete the static NAT command(s).
    • Dynamic NAT: Dynamic NAT has some similarities and differences compared to static NAT. Like static NAT, the NAT router creates a one-to-one mapping between an inside local and inside global address and changes the IP addresses in packets as they exit and enter the inside network. However, the mapping of an inside local address to an inside global address happens dynamically. Dynamic NAT sets up a pool of possible inside global addresses and defines matching criteria to determine which inside local IP addresses should be translated with NAT. The dynamic entry stays in the table as long as traffic flows occasionally. With dynamic NAT, translations do not exist in the NAT table until the router receives traffic that requires translation. Dynamic translations have a timeout period after which they are purged from the translation table.
  • PAT
    • Static PAT: Static PAT translations allow a specific UDP or TCP port on a global address to be translated to a specific port on a local address. Static PAT is the same as static NAT, except that it enables you to specify the protocol (TCP or UDP) and port for the real and mapped addresses. Static PAT enables you to identify the same mapped address across many different static statements, provided that the port is different for each statement. You cannot use the same mapped address for multiple static NAT statements. With static PAT, translations exist in the NAT translation table as soon as you configure static PAT command(s), and they remain in the translation table until you delete the static PAT command(s).
    • NAT Overload or PAT: It is common to hide an entire IP address space, usually consisting of private IP addresses, behind a single IP address (or in some cases a small group of IP addresses) in another (usually public) address space. This type of NAT is called PAT in overload. The dynamic entry stays in the table as long as traffic flows occasionally. With PAT in overload, translations do not exist in the NAT table until the router receives traffic that requires translation. Translations have a timeout period after which they are purged from the translation table.

NAT PAT Configuration Packet Tracer Example #1: Static Source NAT

  • How to translate the 172.16.0.5 IP address to the 10.16.0.5 ip address.
NAT PAT Configuration Packet Tracer
NAT PAT Configuration Packet Tracer

Define the ip nat inside:
Router(config)#interface fa0/0
Router(config-if)#ip nat inside

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Cisco ROMmon Recovery Procedure

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Cisco ROMmon Recovery Procedure:

Today i will discuss cisco rommon recovery procedure step by step. so lets go………..

1. Start the TFTP server (make sure the file path is correct and that you allow both transfer and receive)
2.  Connect to the router via Ethernet cable (an Ethernet cable is preferred due to the large size of the file and the maximum speed that data can travel over the console cable) [boxads]

N.B:  Before the IOS is loaded it is important to make sure that your router has enough memory to support the IOS. The router will allow an IOS to be loaded even if there is not enough memory, in this case a smaller IOS will have to be loaded.

3.   At the rommon prompt enter the following commands (commands are case sensitive, and the use of the directional arrows and tab auto complete function is not allowed):

IP_ADDRESS=IP address of the Ethernet port
IP_SUBNET_MASK=subnet mask of the Ethernet port
DEFAULT_GATEWAY=the default gateway
TFTP_SERVER=the IP of the TFTP server (your local computer)
TFTP_FILE=the file name of the IOS file
tftpdnld

4.   The router will then issue a warning message:

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