Notes on Networking

A blog to share my study notes on Cisco networking and more

TCL Script for DHCP Snooping Configuration

Apr
29

The first script is used to configure 61 Cisco Catalyst 2960S access switches for DHCP Snooping in a way that every switch builds the DHCP Snooping database with its own hostname on the FTP server so that different databases do not overwrite each other.

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EIGRP

Apr
14

TOC

  • EIGRP Process
  • EIGRP Terminology
  • EIGRP Packets
  • Neighborship
  • EIGRP Tables
  • EIGRP Timers
  • Passive Interface
  • EIGRP Re-convergence Process
  • Stub Routers
  • Split Horizon
  • EIGRP Bandwidth Control
  • EIGRP Load Balancing
  • Route Filtering
  • Route Summarization
  • Default Routing
  • Configuration
  • Verification
  • EIGRP Feature Summary

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STP

Apr
07

TOC

  • Concept
  • BPDU Frame
  • STP (802.1d) Process Phases
  • STP Port States
  • Timers
  • STP Topology Changes
  • STP Re-convergence Process
  • Optimizing STP Re-convergence
  • Protecting STP Topology
  • RSTP
  • STP and VLANs (CST, PVST+, MST)

 

Concept

Bridging loops forward a single frame around and around between switches forever.

STP prevents bridging loops by forming a spanning-tree topology in a layer 2 network with redundant links.

STP uses a special layer 2 frame called BPDU to operate.

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First Hop Redundancy Protocols

Apr
01
HSRP VRRP GLBP
Cisco Proprietary IETF Standard Cisco Proprietary
Active / Standby Master / Backup Active Virtual Gateway (AVG)
Active Virtual Forwarders (AVF)
·         AVG assigns virtual MAC addresses to each AVF and answers ARP requests.
·         AVFs forward the traffic. 
Active router selection by priority. The higher, the better.

Default=100 (0~255)

Master router selection by priority. The higher, the better.

Default=100 (1~254)

Active Virtual Gateway selection by Priority/IP Address in group. The higher, the better.

Default=100 (1~255)

Group number (0~255) but usually 16 groups are supported.

HSRP group number is locally significant on interfaces.

Group number (1~255) Group number (0~1023)
HSRP Hello packets        

MC: 224.0.0.2 / UDP: 1945
Hello/Dead time= 3/10 s Default

VRRP Hello packets

MC: 224.0.0.18
Hello/Dead time= 1/3.2 s Default

GLBP Hello packets        

MC: 224.0.0.102 / UDP:3222

Hello/Dead  time= 3/10 s Default

No preemption by default. Preemption by default. No preemption by default.
Interface/object tracking;
HSRP decreases the priority (default=10)
Interface/object tracking;
VRRP decreases the priority
Interface/object tracking;
GLBP decreases the weighting
(default=10)
MAC: 000.0c07.acXX
XX= HSRP group in hex
MAC: 000.5e00.01XX

XX= VRRP group in hex

MAC: 0007.b4XX.XXYY

XXXX=000000xxxxxxxxxx

x…x= Group number in bin

YY= GLBP Forwarder Number in hex

Authentication: MD5/Text Authentication: MD5/Text Authentication: MD5/Text
No load balancing No load balancing Load balancing

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