Category: Protocols

BGP dampening – punishment for unstable BGP prefixes

BGP prefix flapping can be caused by different issues in network. Basically every unstable network where links are unreliably and are going up and down here and there can cause BGP prefix flapping. Every prefix flap will cause some networks to became unreachable. BGP process will then need to recalculate best-path in order to hopefully find other way to get towards unreachable network.

Impact on the network can be enormous as one network prefix missing can mean that huge number of other networks will change the path on which they are reachable. In the situation of prefix flap we have the prefix going up and down all the time. After every status change all those efforts of finding new best-path are done, and when the prefix comes back, everything is calculated again and becomes like before. We have a way to cut the impact of flapping prefixes.

By implementing BGP prefix dampening. When configured, dampening will punish those prefixes that are changing state from reachable to unreachable few time in determined time period. After every flap BGP will give to that prefix a defined penalty of 1000 by default. The penalty points will immediately start to be reduced exponentially but if the prefix flaps more times in little time period he will surely collect enough point to reach Suppress Limit and BGP will at that point mark the prefix as damped. It means that it will immediately suppress the advertisement of the prefix until the penalty points do not fall below Reuse Limit which is 1000 by default. Suppress limit is 2000 by default and yes, there will be needed for prefix to flap three times in order to be suppressed by default (you need to count that the first penalty will be 1000, next one also 1000, but the first one will fall at least by 1 to 999 before second flap occurs.)

PNRP Name Resolution – How it works?

PNRP name resolution protocol uses this two steps:

  • Endpoint determination – In this step the peer is determining the IPv6 address of the computer network card on which the PNRP ID service is published.
  • PNRP ID resolution – After locating and testing the reachability of the peer with the PNRP ID with desired PNRP service, the requesting computer sends a PNRP Request message to that peer for the PNRP ID of the desired service. Other side is sending a reply in which it confirms the PNRP ID of the requested service. It also sends a comment, and up to 4 kilobytes of additional information in that reply. Using the comment and additional 4 kilobytes there can be some custom information sent back to the requestor about the status of server or computer services.

In the process of discovering needed neighbor, PNRP is making an iterative process in which it locates all nodes that have published their PNRP ID. The node performing the resolution is in charge of communicating with the nodes that are closer to the target PNRP ID.


IPSec is basically a way to secure the data transfer between computers. IPSec is making data traffic between two nodes secure by making these things:

  • Data Authentication
    • Authentication – The packets can be spoofed and not sent from the place they seem they are sent. Data origin authentication can be provided with configuration of IPSec. IPSec will enable us to ensure that received packet from a trusted party is really originating from that party.
    • Data integrity – IPSec can be configured to secure that the data packet are not changed when they are crossing the network.
    • Anti-replay protection – IPSec is able to check that the packets received are not duplicates of previous data packets.
  • Encryption
    • IPSec is a technology that enables you to encrypt network data so that it cannot be captured and used by unauthorized persons.

Voice protocols – VoIP protocols

VoIP protocols functionalityThis article will list all well known and famous “voice protocols”. And, also we will shed some light on various things that those protocols are doing that make up a voice over IP network functional.

VoIP Protocols

VoIP networks are very popular these days. In order to support communication between traditional PBXs, Cisco IP phones, analog PSTN, and the analog telephones, all over IP network, quite a number of protocols are needed. Few protocols are indicating protocols (for instance, MGCP, H.323, SIP, H.248, and SCCP) used to position, sustain, and bring down a call. Other protocols are marked at the real voice packets (for example, SRTP, RTCP, and RTP) relatively indicating information. Few of the most common VoIP protocols are shown and described here.

Port Numbers – How does Transport layer identifies the Conversations

Port Numbers – How does Transport layer identifies the Conversations

Computers are today equipped with the whole range of different applications. Almost all of these applications are able in some way to communicate across the network and use Internet to send and get information, updates or check the correctness of user purchase. Consider they all these applications are in some cases simultaneously receiving and sending e-mail, instant messages, web pages, and a VoIP phone calls. In this situation the computer is using one network connection to get all this communication running. But how is it possible that this computer is never confused about choosing the right application that will receive a particular packet? We are talking about the computer that processes two or more communications in the same time for two or more applications running.