Hot Downloads

Welcome, Guest
Username: Password: Remember me

TOPIC: some problem about ccna material (cdpcp - flooding -access l

some problem about ccna material (cdpcp - flooding -access l 10 years 8 months ago #13783

  • faramarz
  • faramarz's Avatar
  • Offline
  • New Member
  • Posts: 1
  • Karma: 0
hi
i need some help 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)?
The administrator has disabled public write access.

Re: some problem about ccna material (cdpcp - flooding -access l 10 years 8 months ago #13819

  • havohej
  • havohej's Avatar
  • Offline
  • Distinguished Member
  • Posts: 152
  • Karma: 0
Hi dude.

Brodcast and flooding??
Is it said that a switch floods broadcast, so it confuses more.


Suposse you are working with a switch with 24 interfaces.
the switch is restarded, and there are three conected hosts : A, B and C.
Assume the switch is restarted with an empty forwarding bridging table.

Host A wants to talk with Host B.

Host A knows the IP address of B, but not the mac, so it performs an ARP to discover the B Mac.
As ARP is broadcast the entire is flooded to all the switch interfaces, including host B, so Host B knows the packet was for him and respond to host A, the switch is listening the conversation and builds the cam table with two entries (for host A and B).

So Broadcast example, the normal arp operation for hosts.
And when Host A wants to talk again with host B it sends it to the swicth, the switch examines the mac destionation, and does not flood only sendind it to the correct destionation port.

To understand flooding, what if a device wants to transmit a packet to a new device after it knows the destion ip and mac address, it send it to the switch, but the switch has no a valid entry in its cam table, it again flood the unicast packet.

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

I have seen it also in ppp serial lines, but never asked why there is a layer 3 ncp for cdp when indeed cdp is a layer 2 protocol, but when doing a show interfaces there is always an ncp open for IP if you are using IP and cdpc if you are using cisco.


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)?

Dont know if you are studyng acls in the ccna courses??
If you are doing so, the topolgoy examples used to explain the acl are very short, but in and out senses when you are using a big topology, when int the input interface you have three or more directly connected routers each with its own lan sending traffic for only this interface, the same applies if you have three or more router directly connected to the same exit interface each one with each differenet subnet destination.

It depends in the politics, sometimes you only want to filter some flows, but the filter not to affect other flows, that cross the same interface.
I think experience will show you why you need in and out acls.
The administrator has disabled public write access.
Time to create page: 0.073 seconds

CCENT/CCNA

Cisco Routers

  • SSL WebVPN
  • Securing Routers
  • Policy Based Routing
  • Router on-a-Stick

VPN Security

  • Understand DMVPN
  • GRE/IPSec Configuration
  • Site-to-Site IPSec VPN
  • IPSec Modes

Cisco Help

  • VPN Client Windows 8
  • VPN Client Windows 7
  • CCP Display Problem
  • Cisco Support App.

Windows 2012

  • New Features
  • Licensing
  • Hyper-V / VDI
  • Install Hyper-V

Linux

  • File Permissions
  • Webmin
  • Groups - Users
  • Samba Setup