I have actually studied from assorted sources that router is a class 3 device. The does routing based upon Network great (layer 3) header, however I have actually a doubt.

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Network resolve translation (NAT) is a attribute of Router i beg your pardon is forced for routing traffic. That does processing based upon both Network layer and also Transport great (layer 4) headers. Therefore why cant we say that router is a class 3 & layer 4 device when it is handling layer 4 header also?



Network deal with translation (NAT) is a attribute of Router which isrequired for routing traffic.

That is totally incorrect. NAT is a kludge (a clumsy, inefficient solution) design to extend the life that IPv4 addressing until IPv6 is ubiquitous. NAT division the IP paradigm that end-to-end connectivity, and many things have troubles with NAT. Routing works quite well there is no NAT. You should only use NAT to be you absolutely have to use it, e.g. Exclusive to publicly addressing, or because that joining 2 networks through overlapping addresses.

It go processing based on both Network layer and also Transport layer(layer 4) headers.

Again, no. Routing does no involve the layer-4 header. One kind of NAT, NAPT (Network address Port Translation), will use the TCP or UDP ports, or ICMP query IDs, yet it only works for those 3 protocols, and also it breaks various other transport protocols and many applications. A routing table (what routers usage to determine the course of packets) has actually nothing around layer-4 protocols in it.

RFC 2663, IP Network deal with Translator (NAT) Terminology and also Considerations defines NAPT:

4.1.2. Network deal with Port translation (NAPT)

NAPT expand the concept of translation one step further by alsotranslating carry identifier (e.g., TCP and UDP port numbers,ICMP ask identifiers). This enables the carry identifiers that anumber of private hosts to it is in multiplexed right into the transportidentifiers that a solitary external address. NAPT allows a collection of hoststo re-publishing a solitary external address. Note that NAPT can be combinedwith an easy NAT so the a swimming pool of outside addresses are offered inconjunction v port translation.

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For packets outbound indigenous the private network, NAPT would translatethe source IP address, resource transport identifier and related fieldssuch together IP, TCP, UDP and ICMP header checksums. Transport identifiercan be one of TCP/UDP harbor or ICMP questions ID. For inbound packets, thedestination IP address, location transport identifier and the IPand move header checksums room translated.