Questions tagged [ipv6]

For questions about Internet Protocol version 6 (IPv6); as specified in RFC 8200.

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95 votes
12 answers
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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,...
Craig Constantine's user avatar
74 votes
5 answers
22k 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,...
mnj's user avatar
  • 851
73 votes
5 answers
33k 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 ...
Vi.'s user avatar
  • 853
47 votes
5 answers
9k 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 ...
Utku's user avatar
  • 754
44 votes
4 answers
53k 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 ...
Craig Constantine's user avatar
39 votes
5 answers
26k 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.
FelixHJ's user avatar
  • 493
38 votes
3 answers
20k views

Why does the IPv6 header not include a checksum?

It is stated in Wikipedia that an IPv6 header does not include a checksum. What are the reasons that were behind this decision?
Paulo Tomé's user avatar
37 votes
5 answers
8k 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 ...
Lorentz Vedeler's user avatar
28 votes
3 answers
6k views

Will IPv6 make private IP addresses become obsolete?

Will it still be useful to make use of private IP addresses with IPv6?
Mit94's user avatar
  • 383
23 votes
3 answers
37k 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 ...
Pue-Tsuâ's user avatar
  • 666
19 votes
4 answers
21k 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 ...
bahamat's user avatar
  • 867
18 votes
6 answers
35k 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 ...
CodyBugstein's user avatar
18 votes
5 answers
16k 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.
Silviu's user avatar
  • 413
18 votes
3 answers
3k 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 ...
User123456's user avatar
17 votes
5 answers
5k views

Why do we need ports with IPv6?

My understanding is there are 2^32 - 1 possible IPv4 addresses, and 2^16 - 1 possible ports. Which gives ~2^48 addresses. The additional 2^16 additional ports seem almost insignificant considering the ...
Josh's user avatar
  • 273
17 votes
5 answers
3k 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 ...
Benjamin A.'s user avatar
  • 1,687
17 votes
2 answers
20k 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?
Tanvir Rahman's user avatar
15 votes
6 answers
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 ...
mdpc's user avatar
  • 925
15 votes
5 answers
14k views

Duplicate IP Address - which one wins?

If there's a duplicate IP address, which one "wins"? First, last, flaps, neither?
Pseudocyber's user avatar
14 votes
3 answers
2k 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 ...
sliebald's user avatar
  • 143
14 votes
4 answers
2k 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 ...
Daniel Jour's user avatar
14 votes
3 answers
6k 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 ...
banjaxed's user avatar
  • 355
14 votes
2 answers
33k 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.)
Axel Kennedal's user avatar
14 votes
1 answer
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?
Waldemar Gałęzinowski's user avatar
14 votes
2 answers
70k views

Stateful vs Stateless IPv6?

What's the difference here? Are stateful IPv6 entries retained in the DHCPv6 server?
stets's user avatar
  • 1,010
13 votes
4 answers
7k views

Difference between :: and ::1

I am confused about following netstat output. There are two kind of local ports. The first is: [::]8100 The second is: [::1]8100 I know that [::1] is a loopback address for IPv6. My question is: ...
Dadash Memmedli's user avatar
13 votes
5 answers
5k 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 ...
Craig Constantine's user avatar
13 votes
3 answers
2k 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 ...
Tim's user avatar
  • 1,545
13 votes
1 answer
3k 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 ?
Benjamin A.'s user avatar
  • 1,687
12 votes
6 answers
4k 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 ...
Morgaine's user avatar
  • 261
12 votes
1 answer
3k 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 ...
Mark Henderson's user avatar
11 votes
4 answers
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?
Lucas Kauffman's user avatar
11 votes
3 answers
698 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 ...
rheone's user avatar
  • 212
11 votes
2 answers
298 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 (...
paraa's user avatar
  • 113
11 votes
2 answers
4k 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 ...
Joren's user avatar
  • 163
10 votes
4 answers
3k 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 ...
Matthias Merkel's user avatar
10 votes
3 answers
7k views

How HTTP is converted to TCP and then how TCP converted to IP?

I know that in Internet Protocol Stack there are actually three layer. They are Application, Internet and Transport. Let's say HTTP in Application layer will be converted to TCP in Transport layer and ...
RajeshKannan's user avatar
10 votes
3 answers
340 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? ...
Craig Constantine's user avatar
10 votes
4 answers
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 ...
SPRBRN's user avatar
  • 221
10 votes
2 answers
6k 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 ...
Craig Constantine's user avatar
10 votes
3 answers
4k 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 ...
Craig Constantine's user avatar
10 votes
1 answer
2k 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 ...
Martin's user avatar
  • 1,229
10 votes
1 answer
3k 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) ...
Tendero's user avatar
  • 321
10 votes
2 answers
937 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 ...
abc's user avatar
  • 203
10 votes
1 answer
18k views

What is the use of the IPv6 scope ID?

In the structure struct sockaddr_in6, the field sin6_scope_id is declared. What is the use of this member? How can we know from the IPv6 address and the prefix length the scope that it should use?
Bionix1441's user avatar
10 votes
1 answer
1k 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-...
Firebirdnz's user avatar
10 votes
1 answer
572 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. ...
Pedro Perez's user avatar
9 votes
2 answers
2k views

Why do IPv6 unique local addresses have to have a /48 prefix?

According to RFC 4193, unique local addresses will always have a prefix of FD00::/8.. but according to Wikipedia: The block fd00::/8 is defined for /48 prefixes, formed by setting the forty least-...
Isaac's user avatar
  • 276
9 votes
2 answers
4k 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 ...
Maximilian Ruta's user avatar
9 votes
4 answers
11k views

Usage of Flow label in IPv6 header?

I have been reading the IPv6 Flow Label Specification (RFC 6437) and I would like to ask about the purpose of setting this label. In case of just using the 2-tuple (source address, destination address)...
Bionix1441's user avatar

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