Is IPV6 Link-Local = IPV4 default gateway ?

[pvanvu]

hi guys , I'm confusing about this problem

I understand the " default gateway " and how it works , but I'm not fully understand about " link-local " in IPV6 , but after many practical LABs , seem like " IPV6 Link-Local and IPV4 default gateway " act the same function , but I'm not 100% sure .


Please help me

thank you

 

[Gryz]

No, it's different.

Default-gateway in IPv4 means: "if I don't have a matching route for the destination, then send a packet via the default-gateway".

IPv6 has exactly the same concept.

Link-local addresses are something completely different. They are a special set of addresses that a host or a router can use for an interface. And they only have significance and uniqueness on the local link. You can use them to talk to your direct neighbors. But you can't use them to talk to routers or hosts that are more than 1 hop away.

Do you know what 10.0.0/8 addresses are ? And what they are used for ? They are called "private addresses". 10/8 and 172.16/16 and 192.168/16 are addresses specially reserved for your private network. You can use them there. But you can't use them to talk to other hosts or routers on the global Internet. (Many people use private addresses in their home-network. But your home-router will convert those addresses in a public-Internet-address when packets leave your home. So those 10/8 addresses will never be seen on the net). Private addresses have only significance in your own private network. Not on the Internet.
https://tools.ietf.org/html/rfc1918

Link-local addresses are something similar. They only have significance on one link between two devices. (Or on one ethernet, between the directly connected hosts and routers).
https://tools.ietf.org/html/rfc4291#section-2.5.6

It seems you have just started trying to learn about networking.
I suggest you get a good book about TCP/IP first. So you understand the basics. And so that the book can give you a proper order in which to learn subjects. If you just start reading random stuff in random order, things can be very confusing.

 

[Red Squirrel]

Also I think link local is only really used in the process of establishing connectivity to the next router/hop/host and maybe used for some housekeeping stuff, but typically not used for actual network communication. ULAs are another type of IPv6 IP range and those are equivalent to the 10.x.x.x and 192.168.x.x ranges in ipv4.

At least that's how I understand it.

 

[pvanvu]

Also I think link local is only really used in the process of establishing connectivity to the next router/hop/host and maybe used for some housekeeping stuff, but typically not used for actual network communication. ULAs are another type of IPv6 IP range and those are equivalent to the 10.x.x.x and 192.168.x.x ranges in ipv4.

At least that's how I understand it.

Thank You Red Squirrel

 

[pvanvu]

No, it's different.

Default-gateway in IPv4 means: "if I don't have a matching route for the destination, then send a packet via the default-gateway".

IPv6 has exactly the same concept.

Link-local addresses are something completely different. They are a special set of addresses that a host or a router can use for an interface. And they only have significance and uniqueness on the local link. You can use them to talk to your direct neighbors. But you can't use them to talk to routers or hosts that are more than 1 hop away.

Do you know what 10.0.0/8 addresses are ? And what they are used for ? They are called "private addresses". 10/8 and 172.16/16 and 192.168/16 are addresses specially reserved for your private network. You can use them there. But you can't use them to talk to other hosts or routers on the global Internet. (Many people use private addresses in their home-network. But your home-router will convert those addresses in a public-Internet-address when packets leave your home. So those 10/8 addresses will never be seen on the net). Private addresses have only significance in your own private network. Not on the Internet.
https://tools.ietf.org/html/rfc1918

Link-local addresses are something similar. They only have significance on one link between two devices. (Or on one ethernet, between the directly connected hosts and routers).
https://tools.ietf.org/html/rfc4291#section-2.5.6

It seems you have just started trying to learn about networking.
I suggest you get a good book about TCP/IP first. So you understand the basics. And so that the book can give you a proper order in which to learn subjects. If you just start reading random stuff in random order, things can be very confusing.

Thank you , Gryz again
I understood everything you just wrote above , maybe I misunderstood about ( Link-local ,and IPv6 Gateway ) , the pic is below . Could you give me some words ?

+ From the left Pic
it says :
Link Local Address : FE80::209...........
IPv6 Gateway : FE80::1

+ From the right Pic
it says : (FE80::1 , FE80::2, FE80::3) are link-local , BUT are used as a Deafault-Gateway in the left Pic

=> so what is the different between Link-Local from the left and the right Pics ( FE80::209........... , and FE80::1 ) ?
=> And why these 3 (FE80::1 , FE80::2, FE80::3) are link-local , but are used as the Gateway ?

I don't quite understand about this . That's what I was asking , but end up asking a wrong question .
That's why I asked " Is IPV6 Link-Local = IPV4 default gateway ? "

I'm currently in CCNA 2 , and this is my biggest confusing question about IPV6 .

Please give me some help ,
Thank you

 

[mv2devnull]

Link-local is not about IPv6; IPv4 has them too. https://en.wikipedia.org/wiki/Link-local_address

The left picture shows that PC-A has address 2001B8:ACAD:A::A and a gateway machine on the same LAN has address FE80::1.

The right picture shows the same data. It does show also the addresses of PC-B, PC-C, R1, R2, and R3.

The R1 is thus the gateway that the PC-A will send all non-local packets to. It has both link-local and public address. (Actually, it has two public addresses, one for each interface.)

You could have similar table in IPv4:

Device Address   Gateway
R1     10.0.0.1  N/A
PC-A   10.0.0.10 10.0.0.1

 

[Gryz]

=> so what is the different between Link-Local from the left and the right Pics ( FE80::209........... , and FE80::1 ) ?

FE80::209 is an address assigned or configured on pc-A.
FE80::1 is an address assigned or configured on router R1.

=> And why these 3 (FE80::1 , FE80::2, FE80::3) are link-local , but are used as the Gateway ?

Note there are three PC and three routers.
The routers are interconnected to each other via 2 serial lines. (R1-R2 and R2-R3).
Each router has a PC connected to it, via a Gigabit Ethernet interface.

As I explained before, if you have a route in your routing-table to a destination, you need to know the outgoing interface.
If the outgoing interface is point-to-point (like a serial interface), it is enough to just know the interface.
If the outgoing interface is a multipoint-interface (like an Ethernet interface), you need to know the next-hop IP-address too.

The only requirement for the next-hop ip-address in a route is that that ip-address is directly connected, and you know how to get to it. Link-local addresses fullfil that requirement. So you can use link-local addresses as a next-hop ip-address without a problem. What else would you have expected as next-hop then ?

 

[pvanvu]

Link-local is not about IPv6; IPv4 has them too. https://en.wikipedia.org/wiki/Link-local_address

The left picture shows that PC-A has address 2001B8:ACAD:A::A and a gateway machine on the same LAN has address FE80::1.

The right picture shows the same data. It does show also the addresses of PC-B, PC-C, R1, R2, and R3.

The R1 is thus the gateway that the PC-A will send all non-local packets to. It has both link-local and public address. (Actually, it has two public addresses, one for each interface.)

You could have similar table in IPv4:

Device Address   Gateway
R1     10.0.0.1  N/A
PC-A   10.0.0.10 10.0.0.1

Thank mv2devnull :thumbsup:

FE80::209 is an address assigned or configured on pc-A.
FE80::1 is an address assigned or configured on router R1.


Note there are three PC and three routers.
The routers are interconnected to each other via 2 serial lines. (R1-R2 and R2-R3).
Each router has a PC connected to it, via a Gigabit Ethernet interface.

As I explained before, if you have a route in your routing-table to a destination, you need to know the outgoing interface.
If the outgoing interface is point-to-point (like a serial interface), it is enough to just know the interface.
If the outgoing interface is a multipoint-interface (like an Ethernet interface), you need to know the next-hop IP-address too.

The only requirement for the next-hop ip-address in a route is that that ip-address is directly connected, and you know how to get to it. Link-local addresses fullfil that requirement. So you can use link-local addresses as a next-hop ip-address without a problem. What else would you have expected as next-hop then ?

Awesome , I got it now ,
Again , Thank Gryz a lot
you are my man ()()()
:thumbsup::thumbsup::thumbsup::thumbsup:

 

[pvanvu]

I'm sorry for asking so many questions , But I still have one last question , hope you are going to give me some words

In Local Organization Network where all the Routers , and Switches are directly connected together by using FastEthernet and Gigabit Ports , Is it necessary to use (RIP , OSPF , EIGRP) or ( Static Route ) in that Local Network ? Or (RIP , OSPF , EIGRP) are used on the Remote Network by using the Serial-Link only ?

I think in the Local-NW , all the devices are directly connected into a LAN , so they already knew the best path to deliver the packets to the Destination after some communications ( like Pinging to each other ) without using any additional Protocols . But i'm wondering do they need (RIP , OSPF , EIGRP) to select the best path among many directly connected Routers ?

 

[Gryz]

In Local Organization Network where all the Routers , and Switches are directly connected together by using FastEthernet and Gigabit Ports ,

That is not always the case.
Some networks are (way) more complicated than that.

Is it necessary to use (RIP , OSPF , EIGRP) or ( Static Route ) in that Local Network ? Or (RIP , OSPF , EIGRP) are used on the Remote Network by using the Serial-Link only ?

FYI, the best IP-routing protocol is IS-IS !!
You left that out of your list, so I thought I should mention it.
(Yes, IS-IS used in all the big ISP- and telco-networks. Enterprise networks more often run OSPF. But IS-IS is technoly-wise the better protocol (imho). I prefer IS-IS over OSPF. By far).

Whether it is necessary to run a routing protocol depends on the topology of the network. The important thing to understand is: routers and hosts know only about directly connected networks (and their ip-prefixes). If a host (host = PC, laptop, server, any device that is not a router) needs to talk to device that it is not directly connected to, it will send the packets to its default-gateway. But for routers it doesn't work that way. They don't have a default-gateway, they need to have routes in their routing table. First they put the prefixes of their directly connected interfaces in their routing table. But if there are more prefixes, of networks they are not directly connected to, they need to learn about those prefixes. Where they are.

network1 --- router --- network2

In this topology, you don't need a routing protocol. Because the router knows about both network1 and network2.

network1 --- router A --- network2 --- router B --- network3.

In this topology you do need a routing protocol. Because router A does not know where network3 is. And router B does not know where network1 is. The routers need to tell each other of network1 and network2. And they do that via a routing protocol.

Of course some human can manually configure static routes. If you do that, you don't need a routing protocol. But in bigger networks, that is not practical. And therefor you do need a routing protocol. Less configuration. And less opportunities to make mistakes.

I think in the Local-NW , all the devices are directly connected into a LAN , so they already knew the best path to deliver the packets to the Destination after some communications ( like Pinging to each other ) without using any additional Protocols . But i'm wondering do they need (RIP , OSPF , EIGRP) to select the best path among many directly connected Routers ?

Yep.
As soon as you have more than 1 network and more than 1 router, you need a routing protocol.

 

[pvanvu]

That is not always the case.
Some networks are (way) more complicated than that.


FYI, the best IP-routing protocol is IS-IS !!
You left that out of your list, so I thought I should mention it.
(Yes, IS-IS used in all the big ISP- and telco-networks. Enterprise networks more often run OSPF. But IS-IS is technoly-wise the better protocol (imho). I prefer IS-IS over OSPF. By far).

Whether it is necessary to run a routing protocol depends on the topology of the network. The important thing to understand is: routers and hosts know only about directly connected networks (and their ip-prefixes). If a host (host = PC, laptop, server, any device that is not a router) needs to talk to device that it is not directly connected to, it will send the packets to its default-gateway. But for routers it doesn't work that way. They don't have a default-gateway, they need to have routes in their routing table. First they put the prefixes of their directly connected interfaces in their routing table. But if there are more prefixes, of networks they are not directly connected to, they need to learn about those prefixes. Where they are.

network1 --- router --- network2

In this topology, you don't need a routing protocol. Because the router knows about both network1 and network2.

network1 --- router A --- network2 --- router B --- network3.

In this topology you do need a routing protocol. Because router A does not know where network3 is. And router B does not know where network1 is. The routers need to tell each other of network1 and network2. And they do that via a routing protocol.

Of course some human can manually configure static routes. If you do that, you don't need a routing protocol. But in bigger networks, that is not practical. And therefor you do need a routing protocol. Less configuration. And less opportunities to make mistakes.


Yep.
As soon as you have more than 1 network and more than 1 router, you need a routing protocol.

Thank you for all the detail explanations , I'll keep them in mind forever
:thumbsup::thumbsup::thumbsup::thumbsup::thumbsup::thumbsup: