Ipv6 general -prefix

ipv6 general-prefix command is a great help when its come to configuration of IPv6 address. As we all know that when IPv6 address are 128 bits which is lengthy. When it comes to configuration of interfaces, we need to key in a long strings of hexadecimal digits. The command will make the configuration less tedious.


Take for example, ISP assigned you an IPv6 address 2003:abcd:1234::/48. Most of your interfaces on the router will most probabaly be configured within this prefix.


ipv6 general-prefix ISPIssued 2003:345:ABCD::/48


So if we want to assigned 2003:345:ABCD::1/64 to interface fa0/1


We just simply need to


int fa0/1
ipv6 address ISPIssued ::1/64


That's it. We don't have to worry that we will mistype the wrong prefix for the IPv6 addresses for all our interfaces. Noted that an interface can have more than one IPv6 addresses, so any mistype will need to be manually removed by the negate command.

IPv6 Configuration

IPv6 Subnetting

An ISP is normally allocated a /32 block.
In Singapore, One of the block issued to Singtel is 2001:0C20::/32

|                  n bits           |       m bits   |            128-n-m bits      |
+-----------------------------+---------------+-------------------------------+
|    global routing prefix | subnet ID   |          interface ID          |
+-----------------------------+---------------+-------------------------------+
An organization is often allocated a /48 block of IPv6 address space.
Let's use 2001:0C20:A::/48 10th group in the subnet assigned to ISP

The remaining 16 bits of the first half 64 bits will give 65536 /64s

Let's use 0000 for loopback address

2001:0C20:A:0000:0000:0000:0000:0000/64

Router Loopback Addresses
Router loopback addresses are /128 bit host routes
2001:0C20:A:0000:0000:0000:0000:0000/64

Each router loopback address is indicated by its Router # (y):
2001:0C20:A:0000:0000:0000:0000:0001/128
2001:0C20:A:0000:0000:0000:0000:0002/128
2001:0C20:A:0000:0000:0000:0000:FFFE/128
2001:0C20:A:0000:0000:0000:0000:FFFF/128

Point-to-Point Addresses 
Point-to-Point are links between only two nodes. 
For such networks, we could use one specific set of networks allocated 
from the prefix 2001:0C20:A:F000:0000:0000:0000:0000/52

Examples of possible Point to Point subnets:
Point-to-Point Link 1
2001:0C20:A:F001:0000:0000:0000:0001/64 
2001:0C20:A:F001:0000:0000:0000:0002/64 
...
Point-to-Point Link 10 
2001:0C20:A:F00A:0000:0000:0000:0001/64 
2001:0C20:A:F00A:0000:0000:0000:0002/64 

Server, Printers Subnet Assignment (Static IP)
For such networks, we could use one specific set of networks allocated from the prefix 2001:0C20:A:E000:0000:0000:0000:0000/52 

These are examples of possible server subnets: 
2001:0C20:A:E001:0000:0000:0000:0000/64  
2001:0C20:A:E002:0000:0000:0000:0000/64 
... 
2001:0C20:A:EFFE:0000:0000:0000:0000/64 
2001:0C20:A:EFFF:0000:0000:0000:0000/64 

General End-Node Subnets 
There are a a few ways you could subnet your end node subnets:  
|          n bits (48)           | b(8) | s(8)  |    128-b-s bits (64)    | 
+-----------------------------+--------------+----------------------------+ 
| global routing prefix    | bldg | Lvl   |         interface ID        | 
+-----------------------------+--------------+----------------------------+ 
OR  
|          n bits (48)           |      v(16)       |      128-v bits (64)     | 
+-----------------------------+----------------+----------------------------+ 
|  global routing prefix   |   VLAN ID   |        interface ID         | 
+-----------------------------+----------------+----------------------------+ 

Building addresses are summarized as: 2001:0C20:A:bb00:0000:0000:0000:0000/56 
Level addresses are: 2001:0C20:A:bbll:0000:0000:0000:0000/64 

Therefore, Building 45, Level 7 would be: 2001:0C20:A:4507::/64

IPv6 Type of Address

A)Link-Local (FE80::/10)
When an IPv6 stack is enabled, link-local address is automatically assigned to each interface. The IPv6 link-local prefix FE80::/10 is used and the interface identifier in Extended Unique Identifier 64 (EUI-64) format is appended as the address's low-order 64-bit. Link-local addresses are only for local-link scope and must never be routed between subnets within a site.

Example

RouterA(config-if)#ipv6 address FE80:0:0:0:1001:1234:5678:00AB link-local

The link-local address is configured here. This command with the link-local argument can be used to override the default link-local address assigned by the router.

You can also enable just IPv6 on an interface without specifying an aggregatable global unicast or site-local address by using the ipv6 enable command, as shown here:

Router(config-if)#ipv6 enable

This command also automatically configures the link-local address on the interface.


B)Site-Local (FEC0::/10) - Deprecated in RFC 3879 and replaced with Unique Local IPv6 Unicast Addresses fc00::/7 - RFC 4193, fd00::/8 localli assigned ULA


A site-local address is used only within a site. Site-local addresses are not enabled by default on nodes like link-local addresses, meaning that they must be assigned.
A site-local address is similar to private address spaces in IPv4. A site-local prefix and address may be assigned to any nodes and routers within a site. However, site-local addresses must never be routed on the global IPv6 Internet.


Usage:Printers,Intranet servers, Network switches, bridges, gateways, wireless access points and any servers and routers that must only be reached internally for management purposes

Example

RouterA(config-if)#ipv6 address FEC0:0:0:1001::1/64

The site-local address is configured on the interface. After the completion of this command, the link-local address is automatically configured.

In the following example, the site-local prefix FEC0:0:0:1001::/64 is used to configure the address. The site-local and link-local addresses are automatically configured:

RouterA(config-if)#ipv6 address FEC0:0:0:1::/64 eui-64

***Take note that the Site-local will appear under the Global Unicast Address field same as Aggregate Global Unicast Address, the only way to know that it is site-local is by the first 4 hexadecimal value FEC0.


C)Aggregatable Global Unicast Address


Each global unicast IPv6 address has three parts:

• Prefix received from a provider— The prefix assigned to an organization by a provider should be at least a /48 prefix. The /48 prefix represents the high-order 48-bit of the network prefix. 
• Site— With one /48 prefix allocated to an organization by a provider, it is possible for that organization to enable up to 65,535 subnets (assignment of 64-bit's prefix to subnets). 
• Host— The host part uses each node's interface identifier. This part of the IPv6 address, which represents the address's low-order 64-bit, is called the interface ID.

Example

RouterA(config-if)#ipv6 address 2001:0c20:0:1001:0:0:0:1abc/64

The aggregatable global unicast address is configured on the interface. After the completion of this command, the link-local address is automatically configured.

In the following example, the aggregatable global unicast prefix 2001:0c20:0:1001::/64 is used to configure the address. The aggregatable global unicast and link-local addresses are automatically configured:

RouterA(config-if)#ipv6 address 2001:0c20:0:1001::/64 eui-64

Static route & floating Static route

Cisco


ip route next-hop address => admin distance of 1

ip route local exit interface => admin distance of 0 like connected interface

e.g. on R1 router

ip route 10.10.30.0 255.255.255.0 10.10.20.2 or

ip route 10.10.30.0 255.255.255.0 s0

** Adding the permanent keyword to a static route statement will keep the static routes in the routing table even if the interface goes down 

floating static route (Backup route)

ip route 10.10.30.0 255.255.255.0 s0

ip route 10.10.30.0 255.255.255.0 s0 91

when running eigrp which has a default AD of 90, eigrp route will appear in routing table and only when that route goes down will the floating static route appear. Serves as a backup route.


Juniper


set routing-options static route 10.10.30.0/24 next-hop 10.10.20.2


IPv6
Cisco - ipv6 route 2001:db8::/32 s0 fe80::1/64
Juniper - set routing-options rib inet6.0 static route 2001:200:20:1::1/128 next-hop 2001:200:30:2::2

Interface configuration

Cisco


Interface (fa0/0 or s0/0/0 etc… …>)

Description (describe link) =>useful for troubleshooting as it can tell you where is it connected to

Ip address (ip address) (subnet mask)

No shut

hint: subnet mask

/32 255.255.255.255 no useful IP address

/31 255.255.255.254 no useful IP address

/30 255.255.255.252 useful for WAN link, 4 IPs (1 network, 1 broadcast, 2 user IPs)

/29 255.255.255.248 8 IPs (1 network, 1 broadcast, 6 user IPs)

/28 255.255.255.240 16 IPs (1 network, 1 broadcast, 14 user IPs)

/27 255.255.255.224 32 IPs (1 network, 1 broadcast, 30 user IPs)

/26 255.255.255.192 64 IPs (1 network, 1 broadcast, 62 user IPs)

/25 255.255.255.128 128 IPs (1 network, 1 broadcast, 126 user IPs)

/24 255.255.255.0

/23 255.255.254.0

/22 255.255.252.0

/21 255.255.248.0

/20 255.255.240.0


Juniper
Interface (fxp0,lo0,em0,fe-x/0/y,se-x/0/y)
x = PIM slot
y = Port Number


inet => IPv4


root@router#set interfaces em0 unit 0 family inet address (ip address)/(prefix)
root@router#commit


IPv6
Cisco - ipv6 address 2001:db8::1/64
Juniper - set interfaces em0 unit 0 family inet6 address 2001:200:30:2::1/64