please help me about some ccna material

faypython

hi
please help me about these que:
1)difference of broadcast & flooding?
2)NCP is for layer 3 packets encap,why we have cdpcp (cdp layer 2)?
3)why we need in & out filter access lists?if we want to filter it
why we should do it after routing decision (just more overhead)?

Humper

faypython wrote:

hi
please help me about these que:
1)difference of broadcast & flooding?
2)NCP is for layer 3 packets encap,why we have cdpcp (cdp layer 2)?
3)why we need in & out filter access lists?if we want to filter it
why we should do it after routing decision (just more overhead)?

I've also been confused by #1, can someone help us out?

Alien

Concerning question #1

A broadcast is a packet that is sent to all the nodes in the network. The act itself broadcasting in networking is transmitting multiple copies of a data to all the nodes within a given network.

Flooding is the mechanism used by switches and bridges to transimit data where by traffic recieved on one interface is sent out on all other interfaces except the interface on which it was recieved.

I'm unable to decipher question #2 and would kindly request you to rephrase it.

Question #3

In access-list is used to block incoming traffic (hackers come to mind) while OUT access-lists are used to block outgoing traffic(inside trying to transfer data out of your company network).
Where the access-list is placed depends on its type. Extended access-lists are placed closer to the source while standard access-lists are placed closer to the destination.

Its been awhile since i took the CCNA and i haven't been reading up on this stuff hence any correction from someone else would be highly welcome incase of error. Hope that helps.

faypython

by OSI model perspective in mind & considering my poor knowledge :
ppp (a layer 2 protocol ) is made of two protocol :
-LCP : link setup ( a layer 2 function )
-NCP : for encapsulation of layer 3 protocols for ex. IPCP , IPXCP ,... ( L3CP )
CDP (also completely layer 2 protocol )
is for discovery of neighbors devices
now i want to know why NCP encapsulate a layer 2 protocol & made CDPCP ?
thank u in advanced

Humper

Alien wrote:

Concerning question #1

A broadcast is a packet that is sent to all the nodes in the network. The act itself broadcasting in networking is transmitting multiple copies of a data to all the nodes within a given network.

Flooding is the mechanism used by switches and bridges to transimit data where by traffic recieved on one interface is sent out on all other interfaces except the interface on which it was recieved.


.

Ok but how is this used in normal switch operation?

twiggy87

Switches will flooding broadcast, multicast and unknown unicast (it's not in the cam table yet) out of all ports except the one it was received on.

A multicast address can never be a source address, so the switch will flood it.
With unknown unicast the switch has no idea where to send the packet so the logical thing to do is to flood it out and hope the destination gets it. Then when the destination replies the switch will record it's mac address and no longer have to flood packets destined for that device. The purpose of a broadcast is to reach everyone anyway so flooding is okay.

LCP and NCP are both components of ppp.

LCP - initiates the connection, and handles a few other tasks like authentication, that kind of thing.

NCP - Negotiates and defines the upper layer protocols that will traverse this connection. most commonly ip

PCHoldmann

One reason to use outbound ACLs is when you want to prevent all traffic from multiple interfaces out a single interface, i.e. prevent port XYZ traffic from 4 departments to the web, but allow it between departments, it might be better to just block it outbound on the internet interface.

lwwarner

faypython wrote:

2)NCP is for layer 3 packets encap,why we have cdpcp (cdp layer 2)?

This is just the way PPP is structured. PPP frames are divided into two basic types, data frames and control frames (LCP, NCP, Auth, etc.). As far as PPP is concerned, *any* protocol that is encapsulated in a PPP data frame is considered a "network-layer" protocol and any configuration that needs to be done for that protocol is done by an NCP.

--Bill