What is the difference between session and flow in networks? In fact, I always visualize flow as a set of packets having the same source and destination. What confuses me is session. So I'd like to know the difference.
Thank you
Networking – Difference Between Session and Flow in Networks
cisconetwork-corerouterswitch
Related Solutions
The description of switches and bridges is "sort of" correct, "sort of" not.
Bridges typically don't have the capability to filter frames. Switches may have the capability to filter, based on things like access control lists, but that's for a bit later in your networking course.
For right now, consider the following:
A bridge forwards frames from one segment to another segment.
A switch is essentially a multi-port bridge.
To answer your true-or-false questions:
Are the following true or false. Correct them if false:
I can only use either a router or a bridge to connect same protocol following multiple >networks (amongst themselves).
False. You'll typically use switches for this task - in much larger networks, you'll use routers and firewalls between geographically separated sites, but that's beyond the scope of your current studies.
All the devices are gateways falling under different layers of OSI model and have ability >to translate between all the protocols of that layer.(for eg. router is a gateway falling >in network layer and is capable of translating protocols TCP followed by network A to UDP >followed by network B (two of the protocols operating at networking layer) and vice versa)
False. Routers examine Layer 3 packets encapsulated inside Layer 2 frames for network information, and then direct them out interfaces according to their destination. In contrast, a switch looks only at the Layer 2 MAC address to determine its destination. A program (Application Layer) which talks with the UDP protocol will only "talk" on that protocol: the router cannot dynamically change it to "TCP" - it doesn't work that way. The router only encapsulates the data in a format which can traverse links between different Layer 3 networks.
Protocols like TCP and UDP operate at OSI Layer 4 - the "Transport" layer, and they differ in very specific ways and are used for different purposes. For example, UDP has no mechanism to detect whether packets are successfully received at the other end - they might get lost! TCP has a mechanism to detect whether data reaches the other end, and if not, to retransmit the lost packets.
A gateway in general operates in application, session and presentation layer.
False. Gateways operate at Layer 3.
Example: We're going to use a typical home network topology.
Computer A in Los Angeles wants to connect to Website B in New York. Computer A performs a DNS lookup of Website A, which translates to an IP address. Computer A sees that the IP address returned is not on the same network as itself, so it sends the packets to its default gateway. The default gateway is usually a router, which contains a routing table, which tells the router which external networks are reachable through which interfaces - it also has a default route which tells the router which interface or IP address to direct traffic to, if the destination does not appear in its routing table. In this case, because it's a consumer-grade appliance connected to a home network, the gateway sends all packets to unknown destinations upstream to the ISP.
Yes, generally you need at least one WAE device for the head-end or Core. For a very simple point to point scenario it is possible to use two routers running Express, but the optimization will be relatively low since DRE won't be used.
As far as I recall the software version in the 1941 is only WAAS Express, which does not save the data to disk. This has major limitations because a feature like DRE which is deduplication needs quite large disk space to work most efficiently. Due to memory limitations, DRE is disabled on the 1921, which further limits the efficiency of the optimization.
The WAE/WAVE appliances are the real deal that provide the full feature set. A while ago Cisco had a few small WAE modules for the first generation ISR's like the 2800. These modules had a CPU and laptop hard drive which provided the required resources for the advanced features.
If you want a minimal and simple Wan Optimization solution, then the WAAS Express could be an option. If the requirement is to reduce network traffic volumes, look for something that stores the deduplication data on disk.
Best Answer
A flow is the data-plane stream of packets between sender and receiver that shares key IP header information. For example, a client at 10.1.1.1 port 12398 communicating with a server at 192.168.1.1 port 22 for SSH is a specific flow that can be captured as the key fields don't change.
A session is the control-plane communication between sender and receiver. The TCP 3-way handshake creates a session that establishes a connection between the sender's source port and receiver's destination listening port. TCP window size, initial sequence and acknowledge values, and keepalives are negotiated as part of building the session.
Basically, flow represents the data-plane and session represents the control-plane.
Edit: Removed bidirectional requirement for a flow.