Saturday , November 18 2017

OSPF virtual link

OSPF virtual link is a tunnel that extends backbone area through a non-backbone area. It is interpreted by the router as unnumbered point-to-point network. Virtual links must be configured between two Area Border Routers. These ABRs are considered neighbours, by establishing the virtual link between them, although they are not linked physically. The transit area (the area through which the virtual link is configured) must have full routing information and cannot be a stub area.

Virtual links add complexity to a network and should be avoided. Use them only as a temporary fix to OSPF topology problem.

Virtual links are used for the following purposes:

  • To link an area to the backbone area through a non-backbone area (most common case). On the picture below Area2 was connected to the Area0 via virtual link, which extends Area0 through transit Area1.

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Huawei eNSP – news

A new version of Huawei Enterprise Network Simulator eNSP was launched few days ago.

What new can we find?

  • Added FTP, HTTP and DNS client and server terminals;
  • Added a function supporting IPv6 to simulate PC.

Besides, a few bugs have been solved.

All details you can find at Huawei Support.

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GRE on Huawei routers

Generic Routing Encapsulation (GRE) is introduced to encapsulate packets. Then these packets can be transmitted over an IPv4 network. GRE provides a mechanism to encapsulate packets of one protocol into packets of another protocol. This allows packets to be transmitted over heterogeneous networks. GRE also provides tunnels to transparently transmit VPN packets. When a device receives a packet that needs to be encapsulated and routed, it adds a GRE header to the packet and encapsulates it into another protocol such as IP. The packet is then forwarded by the IP protocol.

Let’s try to configure GRE tunnel between labnario_1 and labnario_3. All packets sent from PC_1 to PC_2, and vice versa, will be transmitted through the GRE tunnel.

Assure communication between routers in the network. It is omitted here.

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DHCP Relay Agent configuration in Huawei CLI

When PCs are in a different subnet than a DHCP server installed, DHCP Relay Agent can be used to forward DHCP requests from PCs to DHCP server. How to configure DHCP Relay Agent using Huawei CLI?

Let’s assume that we have the following topology:

We want our PC to acquire its IP address from the DHCP server configured on the labnarioR1 router. To do so, labnarioR2 should be configured as a DHCP Relay Agent to forward DHCP Requests and Offers between server and clients.

First, DHCP server should be configured. LabnarioR1 router will be configured to offer DHCP service for PC.

<labnarioR1>system-view 
Enter system view, return user view with Ctrl+Z.
[labnarioR1] dhcp enable
[labnarioR1] ip pool 1
[labnarioR1-ip-pool-1] gateway-list 172.16.1.1
[labnarioR1-ip-pool-1] network 172.16.1.0 mask 255.255.255.0
[labnarioR1-ip-pool-1] dns-list 150.100.15.1 150.100.15.2
[labnarioR1-ip-pool-1] domain-name labnario.com
[labnarioR1-ip-pool-1] quit
[labnarioR1]interface Ethernet0/0/0
[labnarioR1-Ethernet0/0/0]dhcp select global

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VRRP on Huawei router

Virtual Router Redundancy Protocol (VRRP) combines a group of routing devices on a LAN into a backup group that functions as a virtual router. From the host perspective in the LAN, it only needs the IP address of the virtual router rather than the IP address of a specific device in the backup group. Virtual IP address must be set as a default gateway for the host in the LAN. VRRP dynamically associates the virtual router with a physical device that transmits services. When the device fails, the second device is selected to handover traffic. The switchover should be transparent to users, allowing the internal and external networks to communicate without interruption. It, of course, depends on configured services. Most sensitive services need higher reliability and VRRP itself is not enough. But I will mention about it later in the post.

Let’s switch from theory to more practical things.

VRRP topology:

Assure communication between all elements in the network. It is omitted here.

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