Author: Mrityunjay Singh

Posted on

All about MTU and Fragmentation.

Topology

So, in this post we will cover the mtu and fragmentation cases. So, every interface/port have its capacity to send data across the line or port. So, the Maximum transfer unit (MTU).

When I say MTU it usually means at layer 2 frame, but the actual data formation take place at layer 3. So, we have MTU at layer 2 and IP MTU at layer 3.

Bydefault the value of IP MTU is same as MTU, if not defined explicitly. MTU of port may varies depending on the platform or vendor. By default, most of the nodes support 1500 bytes of MTU.

Continue reading “All about MTU and Fragmentation.”

Posted on

GARP(Gratuitous Address resolution Protocol)

Gratuitous ARP is either request or reply packet that is needed in some cases. usually when we assigned any ip on interface or host boot the first packet it send is GARP.

GARP packet have Sender and Target IP address same .Source mac address is of machine whereas destination mac is broadcast.

GARP IMP Question

1)GARP first packet is request or reply ?

2)GARP reply packet is unicast or broadcast ?

3)GARP opcode.

4)Why GARP is used ?

5) Messages or types of GARP packet ?

Learning acrimony—-Total 9 Field

HaPur HaPur SSOTT

In practical environment we only see GARP reply packet no GARP request is send.

https://tools.ietf.org/html/rfc5227#page-15

GARP have two opcode opcode 1 & 2. Remember opcode 1 is used for DAD(duplicate address detection) and opcode 2 is used for GARP.

There is two messages of GARP viz ARP probe (used for DAD) and ARP announcement (used to announce that machine own a particular ip address within the segment.

Consider one example where Switch has PC1 & PC2 and DHCP server connected.

Now PC1 is assigned with 192.168.174.111/24 ip address, PC2 is set to DHCP,

And DHCP server have only one ip i.e 192.168.174.111 left to assigned to PC2, and this ip is already configured on PC1 statically.

So what will DHCP assigned this ip address to PC2 or not.

Ans: DHCP won’t assigned this ip address to PC2 , because DHCP always do ARP probing to check if the ip which dhcp want to assigned is already assigned to any other host in the network or not. Since here 10.10.10.1 is already assigned to PC1 , then DHCP wont’t assigned this ip to PC2.

Now consider if 192.168.174.111 is not assigned to any host on the segment , in this case. DHCP will perform GARP probe message to check if there any duplicity of ip or if the ip that dhcp want to assigned it not used by any host. Let’s assume it is not used by any host, then DHCP will assigned 192.168.174.111 to PC2 and then once the PC2 have ip address assigned by DHCP, PC2 will send GARP announcement message to confirm other that PC2 own 192.168.174.111 ip. In return of GARP announcement it will get no reply which confirm only PC2 own this ip and no other host.

Posted on

BGP Route-Reflector Design

A route learned by one ibgp peer won’t be advertised to another ibgp peer. This is called BGP split horizon rule. This rule is used to avoid loop in ibgp cases.

To mitigate this, we have following option by which one ibgp learned routes can be advertised to another ibgp peer.

  1. BGP full mesh
  2. BGP confederation
  3. BGP route-reflector

In this article we will discuss about the 3rd option i.e BGP route-reflector.

BGP route reflector rule.

Whenever a RR learn route from its client it adds two attributes to the route.

  1. Cluster id – (32-bit identifier, which can be set, by defaults its bgp router-id)
  2. Originator id- (router id of client who send the route)
Continue reading “BGP Route-Reflector Design”
Posted on

Different Static Route Options

The IP assignment on interface is shown as above.

We will demonstrate the following case study.

Case Study 1: Static routes using exit interface

Case Study 2:Static routes using IP as next hop

Case Study 3:Static routes using exit interface and IP add as next hop

Let’s understand how the communication takes place in Ethernet or multi-access networks.

  1. Whenever router want to reach a particular destination, it basically needs two information viz the destination IP address where it wants to go and the L2 address with respect to the destination.
  2. The router must check first whether the outgoing interface is point to point or ethernet/multi-access. In case it is Ethernet then it must resolve L2 address
  3. For getting the L2 address the router must generated ARP request for the destination subset. The router must know on which outgoing interface it needs to generate ARP so the router do routing recursive process to know the outgoing interface for a particular destination.

Continue reading “Different Static Route Options”

Posted on

OSI MODEL

OSI Stands for open system interconnection model.  This is reference or virtual model, you cannot see it , touch it ,but its exists conceptually just like electron, protons etc.

OSI model is invented by ISO(International standard organization). ISO is non profit organization that defines several  standards. It is just like other standard e.g ISI mark, IEEE, CE etc that you must have come across.These standard work for the welfare of society for setting different standard in different areas like food , electronic networks etc.

OSI model have seven layer describe as below.

1)Physical layer

2)Data link layer

3)Network layer

4)Transport layer

5)Session layer

6)Presentation layer

7)Application layer

Continue reading “OSI MODEL”

Posted on

Site to Site IPsec VPN

Topology

Summary:

To implement Flex VPN or IPSEC VPN the topology shown above. The motive is to make the reachability between LAN to LAN network i.e from 20.20.20.0 to 30.30.30.0 & vice versa.

Currently we have configure simple connectivity in which R1 and R2 is reachable to each other via internet cloud.

The basic requirement of any VPN is the rechability between source and destination end point of tunnel.

Continue reading “Site to Site IPsec VPN”

Posted on

Gre Tunnel

Topology

Objectives

Create Gre tunnel between Router A and Router c. We are creating tunnel to internal communication between two LAN segments without, advertising LAN IP in internet domain.

Steps:

  • Your end to end network should be reachable i.e the interface/node from where you are creating tunnel should reachable to destination interface/node. Here Router A ,B & C is configured and running eigrp under internet domain , we have advertised loopback on Router A &C under eigrp.
  • Ping 2.2.2.2 from Router A and 1.1.1.1 from Router C.

Continue reading “Gre Tunnel”

Posted on

MPLS Vpn Working Principle

Topology:

Objective:

Configure MPLS L3VPN and understand it’s working. Currently PE1 & PE2 running iBGP under AS 100.PE1, P1, P2 & PE2 running OSPF as IGP. MPLS backbone running LDP for label distribution, LDP neighbor ship has been established among PE1, P1,P2 and PE2.CE1/CE11 using default routing towards PE1/PE2 respectively.

MPLS VPN used two control plane protocols: LDP and MP-BGP to accomplish MPLS VPN communication.

LDP used for signaling and responsible for distributing label among LSR, however LDP rely on IGP for choosing the best path.MPLS unicast ip forwarding is purely based on IGP and LDP.

Continue reading “MPLS Vpn Working Principle”

Posted on

BGP Over GRE

Topology

Objective:
To implement BGP over GRE , the topology shown above. In topology R1 & R3 running BGP 100 whereas R2 running only IGP.R1-R4 & R3-R5 running ebgp and advertising prefix 4.4.4.4 and 5.5.5.5 respectively.
R1-R2-R3 running ospf under area 0.
Bgp over GRE can be configured in scenario where end to end BGP is not running or where we want to bypass non bgp peer to peering with BGP peer.

Continue reading “BGP Over GRE”