Questions tagged [ipv6]

For questions about Internet Protocol version 6 (IPv6); as specified in RFC2460.

Filter by
Sorted by
Tagged with
91
votes
12answers
28k views

IPv6 address space layout best practices

I'm comfortable with IPv4 address space allocations. By which I mean: Given services to plan for, or an organization to network, I have a good grasp of how to plan IP address space usage. (or at least,...
71
votes
5answers
30k views

Is “IPv10” a joke or a serious RFC draft?

Internet Protocol version 10 (IPv10) Specification The name is funny (IPv4 + IPv6 == IPv10), but the actual proposal looks strange (one more packet format to battle incompatibility between packet ...
60
votes
7answers
17k views

Why are IPv4 addresses running out?

I understand that we are running out (or ran out already?) of IPv4 addresses, but I don't really understand why that is. Right now, every home has its own IPv4 address (dynamically assigned, but still,...
44
votes
5answers
8k views

Why do we need IPv6?

This will be a kind of newbie question but I am not quite sure why we really need IPv6. AFAIK, the story is as follows: In the olden days, when computers were not plentiful, 32 bit IP addresses were ...
43
votes
4answers
44k views

Why is fe80::/10 reserved for link local addresses when fe80::/64 is actually used?

I understand that IPv6 reserves the fe80::/10 prefix for link local addresses, and that hosts select an address with a /64 prefix. Why is the reserved space so much larger than what is actually used ...
38
votes
5answers
7k views

Why does ipv6 specify 128 bit address, when there are only 48 bits in MAC addresses?

So, I'm reading for a networking exam, and I'm just wondering if I have missed something basic. Is there a need for more ip addresses than MAC addresses, and how would a node with one network adapter ...
22
votes
4answers
10k views

What is the proper term for ipaddress/hostname:port

What is the proper term for (example) hostname.tld:433 (hostname:portnumber)? It is not just hostname, and it is not really a URL either :) same goes for 10.0.0.1:3306 etc.
18
votes
3answers
1k views

How does multihoming work with ipv6?

What are the differences between multihoming in IPv4 versus IPv6? Can an enterprise request a provider-independent IPv6 address space from its RIR/LIR which can be advertised to multiple upstream ...
16
votes
4answers
14k views

IPv6: Why not use /126 on P2P links for IPv6?

In IPv4 we use /30 to conserve addresses. So why do some people recommend using /64 on P2P links instead of /126? I get using a /64 on regular subnets but isn't using a /64 when there will only ever ...
16
votes
5answers
2k views

How to choose a BGP router ID when using IPv6 only?

Usually, when using BGP, you can choose (or your device chooses four you) a router ID from one of your assigned public IP addresses. Now, let's admit you only run IPv6. As the router ID is still a 32 ...
15
votes
6answers
1k views

Time to switch to IPv6?

I am thinking of upgrading our networking situation and am considering a migration of IPv4 to IPv6. Is it too soon to be considering this move as it looks like much of the networking gear and OSen ...
14
votes
6answers
23k views

How are IP addresses mapped to MAC addresses?

I've been reading about the differences between MAC and IP addresses, and why we need both of them. To summarize, MAC addresses are physical unchangeable unique IDs for every single device while IP ...
14
votes
5answers
9k views

Duplicate IP Address - which one wins?

If there's a duplicate IP address, which one "wins"? First, last, flaps, neither?
13
votes
3answers
1k views

Where can I use the IPv6 documentation prefix

We are currently building a networking course with a practical part where students have to configure a small network in a virtual environment. However, we are not sure what ipv6 prefixes we can use ...
13
votes
4answers
1k views

Possible (bit) patterns of a netmask

Given a prefix Y, it's easy to calculate the corresponding netmask: Put Y times a set bit, and then fill up "to the right" with zeros until one has 32 bits (IPv4) in total. Example: Prefix 24, thus ...
13
votes
1answer
1k views

What happened to IPv5?

I hear/read much about IPv4 and IPv6 and nothing about IPv5. Where did it get lost in the discussion?
12
votes
6answers
3k views

Best practice for dual-homing site with two ISPs?

I am subscribed to two ISPs, a fast expensive one and a cheap but slower one. They use different technologies, cable and ADSL, so there isn't much of a single point of failure, and all my comms ...
12
votes
5answers
4k views

What IPv6 prefixes should never be routed?

Seems clear to me that the Link Local, and Unique Local, addresses should at least be filtered. Is there anything other than LLA/ULA that should be filtered? For LLA, is it standard practice to ...
12
votes
3answers
1k views

Are the IPv6 address space and IPv4 address space completely disjoint?

Tanenbaum's Computer Networks says Finally, IPv4 addresses can be written as a pair of colons and an old dotted decimal number, for example: ::192.31.20.46 Does it mean the IPv4 address space ...
12
votes
1answer
2k views

What is the maximum prefix size routed in the IPv6 Internet?

In v4, most of the operators filter BGP updates for prefixes longer than a /24, to preserve the size of the full view. What about IPv6 ? Is there such "convention" that stands out ?
12
votes
1answer
2k views

ASA5505 and IPv6 over a PPPoE Link

I see a lot of conflicting information about whether or not a Cisco ASA (5505 in this case) can use IPv6 over a PPPoE connection. I see official Cisco documentation making it look easy, but I see ...
11
votes
4answers
8k views

Why is the U/L bit inversed in EUI64?

This inversion is bijective, so I can't figure out what is it's use.
11
votes
3answers
3k views

Should a router use SLAAC for IPv6 address assignment?

I am a little confused by the following 2 RFCs relating to IPv6: RFC 4862 (IPv6 Stateless Address Autoconfiguration) RFC 7084 (IPv6 CE Router Requirements) RFC 4862 states: The autoconfiguration ...
11
votes
2answers
230 views

IPv6 Subnetting - Block RA on Switches?

I'm currently planning a v6 only small datacenter network. Imagine for now one deployment consisting of 6 racks with 12 servers per rack. Each server has 2 NICs for two physically separate networks (...
11
votes
2answers
3k views

IPv6 DHCP Server vs Router

I am setting up a testing environment for dualstack. I currently have a server (Windows 2008 R2), 2 switches and a router installed and configured. The server is the Primary Domain Controller and it ...
10
votes
4answers
1k views

Migration from IPv4 to IPv6 strategies

As everyone is aware we are out of IPv4 addresses and soon (if not already) we shall be moving on to IPv6. What are some good strategies and practices to migrate a complete IPv4 network onto IPv6?
10
votes
4answers
2k views

Using IP subnet at multiple datacenters

We control IPv4 and IPv6 subnets. Now we'd like to use a part of a /24 IPv4 subnet at one datacenter and another part at another datacenter. I know that announcing the subnet on the internet at ...
10
votes
4answers
1k views

IPv4 shortage is now becoming a reality - what is needed for IPv6 to work?

Today I read that Microsoft has no more IPv4 addresses for its Azure cloud. Earlier this week I read that Latin America is out of IPv4 addresses as well. These are real - not predicted - IPv4 address ...
10
votes
3answers
3k views

Selecting IPv6 Unique Local Addresses (ie, choosing least-sig 40 bits)

We started with fec0::/10 for site-local addresses -- but that is now deprecated. Instead, we now have fc00::/7 reserved, with fd00::/8 dedicated to /48 nets for Unique Local Addresses. What's the ...
10
votes
1answer
2k views

Does IP provide QoS or not?

IP provides a best-effort delivery service. I believe this implies, among other things, that it offers no QoS to the users. However, IP has a byte in its headers (ToS in v4 and Trafic Class in v6) ...
10
votes
2answers
791 views

ipv6 Aggregatable global unicast addresses

Studying IPv6 addressing I haven't understood IPv6 aggregable global unicast addresses, I mean on RFC 4291 there is a generic scheme: | n bits | m bits | 128-n-m bits ...
10
votes
2answers
427 views

What is the proper name for hexadecimal like standard notation of an IPv6 address?

RFCs such as 5952 - "A Recommendation for IPv6 Address Text Representation" and 2373 - "IP Version 6 Addressing Architecture" each outline the commonly used hexadecimal and colon based notation that ...
10
votes
1answer
486 views

Dynamic Crypto Map with IPv6 access list

I am trying to configure a dynamic crypto map for use on a pure IPv6 network, on Cisco 15.2M. The problem is when I try to add an ipv6 access list to the dynamic crypto map, I get an error message. ...
9
votes
3answers
286 views

Mitigating bad/malicious IPv6 RA announcements

In a Cisco environment (ISR-G2), how do I prevent, or mitigate, incorrect RA announcements? I see Cisco has "IPv6 RA Guard"... But does that just run on the router and "fight back" with correct RAs? ...
9
votes
1answer
1k views

What happens when a subnet reaches capacity?

Other than not being able to claim any more IP addresses in a subnet, what other bad things happen when a subnet reaches 100% utilization, if anything?
9
votes
3answers
20k views

What is Link-local addressing?

I noticed that IPv4 reserved 169.254.0.0/16 and IPv6 reserved fe80::/10 for link-local addressing. While I saw IPv6 uses both fe80::/10 address and my private IPv6 address fd00::12 to communicate with ...
9
votes
3answers
1k views

ipv6 addressing /127 vs eui-64

Best practice is to use a manual /127 address for point to point addressing described here RFC2373 for EUI-64 ERFC 2373 dictates the conversion process, which has two steps. The first is to convert ...
9
votes
2answers
17k views

IPv6 link-local vs unique local

When do you use link-local or unique local in IPv6 networks? (Cisco doesn't manage to explain it properly in their online material.)
9
votes
2answers
5k views

Is TCP maximum segment size (MSS) “clamping” compatible with IPv6?

With IPv4, TCP MSS "clamping" (a network device editing the MSS value in a TCP header) can help when path maximum transmission unit discovery is not working. (e.g., when ICMP is being blocked ...
9
votes
1answer
979 views

What is the use-case of including the IPv4 address in IPv6 address?

It is possible to include the IPv4 address into IPv6 address. For example, 2001:db8::c0a8:6301 where last 32 bits are IPv4 address 192.168.99.1. There is even a special notation of IPv6 address where ...
9
votes
2answers
4k views

Configure External Interface for DHCPv6 client on Cisco IOS

What are the necessary steps to configure IOS 12.4(25f) to support IPv6? Comcast is the ISP, and I'll be using a Server 2012 box for internal DHCPv6. I'll need to grab a DHCPv6 address from Comcast ...
9
votes
2answers
2k views

Are IPv6 Wildcard Matches in Cisco IOS Possible?

Facebook is very clever with their IPv6 address scheme, but it got me thinking about ACLs and Is it possible to write a Cisco IOS IPv6 ACL that matches ? In IPv4 you could match a middle octet such as ...
9
votes
1answer
1k views

Blocking IPv6 RA advertisements on Juniper EX series switch

How do I go about blocking IPv6 RA advertisements on access ports on a Juniper EX series switch? I know that Cisco offers ra-guard as an option much like bpdu-guard on spanning tree, I am just not ...
8
votes
6answers
4k views

Could IPv6 make NAT / port numbers redundant?

From what I can tell, each process could get its own IP address, with loads of IP's to spare. What would the drawbacks be? Essentially, your host would become a router and each process is a host (in ...
8
votes
2answers
3k views

What are common sizes to split a /29 - /32 IPv6 subnet?

As an LIR, you are getting a /29 to /32 network allocation by the RIPE, but I am a bit overwhelmed by the size of this subnet, and don't find a starting point to split this into common sizes. What we ...
8
votes
2answers
7k views

Is it true that the fd00::/8 address range (ULA) in ipv6 is for machines that you NEVER want to speak with anything on the Internet?

Is it true that the fd00::/8 address space (User Local Addresses) in ipv6 is for machines that you NEVER want to speak with anything on the Internet? I was just reading that here and rather surprised ...
8
votes
2answers
10k views

Why don't we use MAC address instead of IP for having “Internet” or doing communication? [duplicate]

We know MAC address is unique in each devices.So why can't we just send/receive data using MAC address only?
8
votes
1answer
1k views

What is the meaning of streamlined ipv6 header?

I don't understand what it is meant for "streamlined ipv6 header"? Could you please provide an example?
8
votes
2answers
3k views

IPv6 RA SLAAC prefix lifetime

From what I understand, there is no way to change the prefix lifetime once hosts install the prefix. If I shorten the valid/preferred timer for a prefix, it has no effect on hosts already using the ...
8
votes
1answer
736 views

Cisco IPv6 BNG Radius Attributes

I am trying to push out IPv6 unnumbered to an interface via radius. I am trying to do it in a similar fashion to how you would for IPv4: Cisco-AVPair += "ip:vrf-id=vrf-name", Cisco-AVPair += "ip:ip-...