IP+Services

=DHCP= toc

Routers can server DHCP in two ways:


 * 1) Forwarding DHCP request via a helper address: **#ip helper-address 10.1.1.1**
 * 2) Configuration of an actual DHCP server on the router itself.

The following is a sample DHCP service configuration:

//**#ip dhcp pool **// //**#network 10.1.1.1 255.255.255.0**// //**#dns-server 10.1.1.2**// //**#default-router 10.1.1.254**// //**#lease 0 0 20**//

=Redundancy and Load Balancing=

HSRP
Used to ensure redundancy among default gateways. Allows multiple routers to share a single virtual IP address. Key features are:


 * Virtual IP (Must be unique) and MAC address (0000.0C07.ACxx, where xx is the HSRP group)
 * //**#standby 21 ip 10.1.1.25**//
 * 3 second hello, 10 second dead interval sent by the active router
 * Highest priority determines active router. Pre-empt disabled by default
 * //**#standby 21 priority 120**//
 * //**#standby 21 preempt**//
 * Supports the ability to track interfaces and decrease priority when a tracked interface fails
 * //**#standby 21 track serial 2/1**//
 * Up to 255 groups per interface allow for load balancing

VRRP
This is the IEEE standardized solution for HSRP


 * Virtual multicast mac is 0000.5E00.01xx
 * Does not support interface tracking
 * Default is to preempt
 * Master=active

GLBP
Similar to VRRP, but it uses a group of up to 4 possible routers, assigning them each a unique mac address (0007.B400.xxyy). When a device ARPs for the VIP, GLBP will reply with any of the 4 MACs to ensure load balancing.

NTP
Stratum 1 is best. The following are sample configurations:

//**#ntp authenticate**// //**#ntp trusted-key 1**//
 * **if#ntp broadcast**: Causes NTP updates to be sent from configured interface
 * //**#ntp master 7: Configures device to be a stratum level 7**//
 * //**#ntp authentication-key 1 md5 1514190900 7**//
 * //**#ntp sever 10.1.1.1**//
 * //**#ntp broadcast client**//
 * //**#ntp peer 10.1.1.1**//