]> CableLabs

858 Coal Creek Circle Louisville CO 80027 USA c.donley@cablelabs.com

Time Warner Cable

13241 Woodland Park Rd Herndon VA 20171 USA william.howard@twcable.com

Rogers Communications

8200 Dixie Road Brampton ON L6T 0C1 Canada victor@jvknet.com

CableLabs

858 Coal Creek Circle Louisville CO 80027 USA j.berg@cablelabs.com

Juniper Networks

1194 N. Mathilda Ave Sunnyvale CA 94089 USA jineshd@juniper.net

CGN NAT444 DS-Lite Dual-Stack Lite IPv4 NAT IPv6 LSN transition NAT444 is an IPv4 extension technology being considered by Service Providers as a means to continue offering IPv4 service to customers while transitioning to IPv6. This technology adds an extra Carrier-Grade NAT (CGN) in the Service Provider network, often resulting in two NATs. CableLabs, Time Warner Cable, and Rogers Communications independently tested the impacts of NAT444 on many popular Internet services using a variety of test scenarios, network topologies, and vendor equipment. This document identifies areas where adding a second layer of NAT disrupts the communication channel for common Internet applications. This document was updated to include the Dual-Stack Lite (DS-Lite) impacts also.

IANA, APNIC, and RIPE NCC exhausted their IPv4 address space in 2011-2012. Current projections suggest that ARIN may exhaust its free pool of IPv4 addresses in 2013. IPv6 is the solution to the IPv4 depletion problem; however, the transition to IPv6 will not be completed prior to IPv4 exhaustion. NAT444 and Dual-Stack Lite are transition mechanisms that will allow Service Providers to multiplex customers behind a single IPv4 address, which will allow many legacy devices and applications some IPv4 connectivity. While both NAT444 and Dual-Stack Lite provide basic IPv4 connectivity, they impact a number of advanced applications. This document describes suboptimal behaviors of NAT444 and DS-Lite found in our test environments. From July through August 2010, CableLabs, Time Warner Cable, and Rogers Communications tested the impact of NAT444 on common applications using Carrier-Grade NAT (CGN) devices. This testing was focused on a wide array of real-time usage scenarios designed to evaluate the user experience over the public Internet using NAT444 in both single and dual ISP environments. The purpose of this testing was to identify applications where the technology either breaks or significantly impacts the user experience. The testing revealed that applications, such as video streaming, video gaming, and peer-to-peer file sharing, are impacted by NAT444. From June through October 2011, CableLabs conducted additional testing of CGN technologies, including both NAT444 and Dual-Stack Lite. The testing focused on working with several vendors including A10, Alcatel-Lucent, and Juniper to optimize the performance of those applications that experienced negative impacts during earlier CGN testing and to expand the testing to DS-Lite. Applications that were tested included, but were not necessarily limited to, the following: Video/Audio streaming, e.g., Silverlight-based applications, Netflix, YouTube, Pandora 2 Peer-to-peer applications, e.g., video gaming, uTorrent Online gaming, e.g., Xbox Large file transfers using File Transfer Protocol (FTP) Session Initiation Protocol (SIP) calls via X-Lite, Skype Social Networking, e.g., Facebook, Webkinz Video chat, e.g., Skype Web conferencing

The diagrams below depict the general network architecture used for testing NAT444 and Dual-Stack Lite coexistence technologies at CableLabs.

This is a typical case for a client accessing content on the Internet. For this case, we focused on basic web browsing, voice and video chat, instant messaging, video streaming (using YouTube, Google Videos, etc.), torrent leeching and seeding, FTP, and gaming.

This is similar to Case 1, except that two clients are behind the same Large-Scale NAT (LSN) and in the same home network. This test case was conducted to observe any change in speed in basic web browsing and video streaming.

In this scenario, the two clients are under the same LSN but behind two different gateways. This simulates connectivity between two residential subscribers on the same ISP. We tested peer-to-peer applications.

This test case is similar to Case 1 but with the addition of another identical ISP. This topology allows us to test traffic between two residential customers connected across the Internet. We focused on client-to-client applications such as IM and peer-to-peer.

The lab environment was intended to emulate multiple Service Provider networks with a CGN deployed and with connectivity to the public IPv4 or IPv6 Internet (as dictated by the coexistence technology under test). This was accomplished by configuring a CGN behind multiple cable modem termination systems (CMTSs) and setting up multiple home networks for each ISP. Testing involved sending traffic to and from the public Internet in both single and dual ISP environments, using both single and multiple home networks. The following equipment was used for testing: CGN CMTS Cable Modem (CM) IP sniffer RF (radio frequency) sniffer Metrics tools (for network performance) CPE (Customer Premises Equipment) gateway devices Laptop or desktop computers (multiple OSs used) Gaming consoles iPad or tablet devices other Customer Edge (CE) equipment, e.g., Blu-ray players supporting miscellaneous applications One or more CPE gateway devices were configured in the home network. One or more host devices behind the gateways were also configured in order to test conditions, such as multiple users on multiple home networks in the CGN architecture, both in single and dual ISP environments. The scope of testing was honed down to the specific types of applications and network conditions that demonstrated a high probability of diminishing user experience based on prior testing. The following use cases were tested: Video streaming over Netflix Video streaming over YouTube Video streaming over Joost Online gaming with Xbox (one user) Peer-to-peer gaming with Xbox (two users) BitTorrent/uTorrent file seeding/leeching Pandora Internet Radio FTP server Web conferencing GoToMeeting (GTM), WebEx Social Networking -- Facebook, Webkinz (chat, YouTube, file transfer) Internet Archive -- Video and Audio streaming; large file downloads Video streaming using iClips SIP Calls -- X-Lite, Skype, PJSIP Microsoft Smooth Streaming (Silverlight) Video chat -- Skype, OoVoo The following CPE devices were used for testing these applications on one or more home networks: Windows 7, XP, and Vista-based laptops MAC OS X laptop iPad Xbox gaming consoles iPhone and Android smartphones LG Blu-ray player (test applications such as Netflix, Vudu, etc.) Home routers -- Netgear, Linksys, D-Link, Cisco, Apple

Metrics data that were collected during the course of testing were related to throughput, latency, and jitter. These metrics were evaluated under three conditions: Initial finding on the CGN configuration used for testing Retest of the same test scenario with the CGN removed from the network Retest with a new configuration (optimized) on the CGN (when possible) In our testing, we found only slight differences with respect to latency or jitter when the CGN was in the network versus when it was not present in the network. It should be noted that we did not conduct any performance testing and metrics gathered were limited to single session scenarios. Also, bandwidth was not restricted on the Data Over Cable Service Interface Specification (DOCSIS) network. Simulated homes shared a single DOCSIS upstream and downstream channel. Case Avg Latency Min Latency Max Latency RFC 4689 Absolute Avg Jitter Max Jitter With CGN 240.32 us 233.77 us 428.40 us 1.86 us 191.22 us Without CGN 211.88 us 190.39 us 402.69 us 0.07 us 176.16 us Note: Performance testing as defined by CableLabs includes load testing, induction of impairments on the network, etc. This type of testing was out of scope for CGN testing.

The following test scenarios were executed using the aforementioned applications and test equipment: Single ISP, Single Home Network, with Single User Single ISP, Two Home Networks, with One User on Each Network Dual ISPs, Single Home Network, with Single User on Each ISP Dual ISPs, One Home Network, with One User connected to ISP-A; Two Home Networks, with One User on Each connected to ISP-B These test scenarios were executed for both NAT444 and DS-Lite technologies.

The CGN was configured for the optimal setting for the specific test being executed for NAT444 or DS-Lite. Individual vendors provided validation of the configuration used for the coexistence technology under test prior to the start of testing. Some NAT444 testing used private IPv4 space between the CGN and CPE router; other tests used public (non-) IPv4 space between the CGN and CPE router. With the exception of 6to4 traffic, we observed no difference in test results whether private or public address space was used. 6to4 failed when public space was used between the CGN and the CPE router was public, but CPE routers did not initiate 6to4 when private space was used. CPE gateways and client devices were configured with IPv4 or IPv6 addresses using DHCP or manual configuration, as required by each of the devices used in the test. All devices were brought to operational state. Connectivity of CPE devices to provider network and public Internet was verified prior to the start of each test. IP sniffers and metrics tools were configured as required before starting tests. IP capture and metrics data was collected for all failed test scenarios. Sniffing was configured behind the home routers, north and south of the CMTS, and north and south of the CGN. The test technician executed test scenarios listed above, for single and dual ISP environments, testing multiple users on multiple home networks, using the applications described above where applicable to the each specific test scenario. Results and checklists were compiled for all tests executed and for each combination of devices tested.

CGN testing revealed that basic services such as email and web browsing worked normally and as expected. However, there were some service-affecting issues noted for applications that fall into two categories: dropped service and performance impacted service. In addition, for some specific applications in which the performance was impacted, throughput, latency, and jitter measurements were taken. We observed that performance often differs from vendor to vendor and from test environment to test environment, and the results are somewhat difficult to predict. So as to not become a comparison between different vendor implementations, these results are presented in summary form. When issues were identified, we worked with the vendors involved to confirm the specific issues and explore workarounds. Except where noted, impacts to NAT444 and DS-Lite were similar. In 2010 testing, we identified that IPv6 transition technologies such as 6to4 and Teredo fail outright or are subject to severe service degradation. We did not repeat transition technology testing in 2011. Note: While email and web browsing operated as expected within our environment, there have been reports that anti-spam/anti-abuse measures limiting the number of connections from a single address can cause problems in a CGN environment by improperly interpreting address sharing as too many connections from a single device. Care should be taken when deploying CGNs to mitigate the impact of address sharing when configuring anti-spam/anti-abuse measures. See Section 3.4.

Several peer-to-peer applications, specifically peer-to-peer gaming using Xbox and peer-to-peer SIP calls using the PJSIP client, failed in both the NAT444 and Dual-Stack Lite environments. Many CGN devices use "full cone" NAT so that once the CGN maps a port for outbound services, it will accept incoming connections to that port. However, some applications did not first send outgoing traffic and hence did not open an incoming port through the CGN. Other applications try to open a particular fixed port through the CGN; while service will work for a single subscriber behind the CGN, it fails when multiple subscribers try to use that port. PJSIP and other SIP software worked when clients used a registration server to initiate calls, provided that the client inside the CGN initiated the traffic first and that only one SIP user was active behind a single IPv4 address at any given time. However, in our testing, we observed that when making a direct client-to-client SIP call across two home networks on a single ISP, or when calling from a single home network across dual ISPs, calls could neither be initiated nor received. In the case of peer-to-peer gaming between two Xbox 360 users in different home networks on the same ISP, the game could not be connected between the two users. Both users shared an outside IP address and tried to connect to the same port, causing a connection failure. There are some interesting nuances to this problem. In the case where two users are in the same home network and the scenario is through a single ISP, when the Xbox tries to register with the Xbox server, the server sees that both Xboxes are coming through the same public IP address and directs the devices to connect using their internal IP addresses. So, the connection ultimately gets established directly between both Xboxes via the home gateway, rather than the Xbox server. In the case where there are two Xbox users on two different home networks using a single ISP and the CGN is configured with only one public IPv4 address, this scenario will not work because the route between the two users cannot be determined. However, if the CGN is configured with two public NAT IP addresses, this scenario will work because now there is a unique IP address with which to communicate. This is not an ideal solution, however, because it means that there is a one-to-one relationship between IP addresses in the public NAT and the number of Xbox users on each network. Update: in December 2011, Microsoft released an update for Xbox. While we did not conduct thorough testing using the new release, preliminary testing indicates that Xboxes that upgraded to the latest version can play head-to-head behind a CGN, at least for some games. Other peer-to-peer applications that were noted to fail were seeding sessions initiated on Bittorent and uTorrent. In our test, torrent seeding was initiated on a client inside the CGN. Leeching was initiated using a client on the public Internet. It was observed that direct peer-to-peer seeding did not work. However, the torrent session typically redirected the leeching client to a proxy server, in which case the torrent session was set up successfully. Additionally, with the proxy in the network, re-seeding via additional leech clients worked as would be expected for a typical torrent session. Finally, uTorrent tries to use Session Traversal Utilities for NAT (STUN) to identify its outside address. In working with vendors, we learned that increasing the STUN timeout to 4 minutes improved uTorrent seeding performance behind a CGN, resulting in the ability for the uTorrent client to open a port and successfully seed content. FTP sessions to servers located inside the home (e.g., behind two layers of NAT) failed. When the CGN was bypassed and traffic only needed to flow through one layer of NAT, clients were able to connect. Finally, multicast traffic was not forwarded through the CGN.

Large size file transfers and multiple video streaming sessions initiated on a single client on the same home network behind the CGN experienced reduced performance in our environment. We measured these variations in user experience against a baseline IPv4 environment where NAT is not deployed. In our testing, we tried large file transfers from several FTP sites, as well as downloading sizable audio and video files (750 MB to 1.4 GB) from the Internet Archive. We observed that when Dual-Stack Lite was implemented for some specific home router and client combinations, the transfer rate was markedly slower. For example, PC1 using one operating system behind the same home router as PC2 using a different operating system yielded a transfer rate of 120 kbps for PC1, versus 250 kbps for PC2. Our conclusion is that varying combinations of home routers and CE-client devices may result in a user experience that is less than what the user would expect for typical applications. It is also difficult to predict which combinations of CPE routers and CE devices will produce a reduced experience for the user. We did not analyze the root cause of the divergence in performance across CE devices, as this was beyond the scope of our testing. However, as this issue was specific to Dual-Stack Lite, we suspect that it is related to the MTU. While video streaming sessions for a single user generally performed well, testing revealed that video streaming sessions such as Microsoft Smooth Streaming technology (i.e., Silverlight) or Netflix might also exhibit some service impacting behavior. In particular, this was observed on one older, yet popular and well-known CPE router where the first session was severely degraded when a second session was initiated in the same home network. Traffic from the first session ceased for 8 s once the second session was initiated. While we are tempted to write this off as a problematic home router, its popularity suggests that home router interactions may cause issues in NAT444 deployments (newer routers that support DS-Lite were not observed to experience this condition). Overall, longer buffering times for video sessions were noted for most client devices behind all types of home routers. However, once the initial buffering was complete, the video streams were consistently smooth. In addition, there were varying degrees as to how well multiple video sessions were displayed on various client devices across the CPE routers tested. Some video playback devices performed better than others.

Since CableLabs completed initial CGN testing in 2010, there have been quantifiable improvements in performance over CGN since that time. These improvements may be categorized as follows: Content provider updates Application updates Improvements on the CGNs themselves In terms of content provider updates, we have noted improvements in the overall performance of streaming applications in the CGN environment. Whereas applications such as streaming video were very problematic a year ago with regard to jitter and latency, our most recent testing revealed that there is less of an issue with these conditions, except in some cases when multiple video streaming sessions were initiated on the same client using specific types of home routers. Applications such as MS Smooth Streaming appear to have addressed these issues to some degree. As far as application updates, use of STUN and/or proxy servers to offset some of the limitations of NAT and tunneling in the network are more evident as workarounds to the peer-to-peer issues. Applications appear to have incorporated other mechanisms for delivering content faster, even if buffering times are somewhat slower and the content is not rendered as quickly. CGN vendors have also upgraded their devices to mitigate several known issues with specific applications. With regard to addressing peer-to-peer SIP call applications, port reservations appear to be a workaround to the problem. However, this approach has limitations because there are limited numbers of users that can have port reservations at any given time. For example, one CGN implementation allowed a port reservation to be made on port 5060 (default SIP port), but this was the only port that could be configured for the SIP client. This means that only one user can be granted the port reservation.

There are other challenges that arise when using shared IPv4 address space, as with NAT444. Some of these challenges include: Loss of geolocation information - Often, translation zones will cross traditional geographic boundaries. Since the source addresses of packets traversing an LSN are set to the external address of the LSN, it is difficult for external entities to associate IP/Port information to specific locations/areas. Lawful Intercept/Abuse Response - Due to the nature of NAT444 address sharing, it will be hard to determine the customer/endpoint responsible for initiating a specific IPv4 flow based on source IP address alone. Content providers, Service Providers, and law enforcement agencies will need to use new mechanisms (e.g., logging source port and timestamp in addition to source IP address) to potentially mitigate this new problem. This may impact the timely response to various identification requests. See . Anti-spoofing - Multiplexing users behind a single IP address can lead to situations where traffic from that address triggers anti-spoofing/DDoS-protection mechanisms, resulting in unintentional loss of connectivity for some users. We have received reports of such anti-spoofing/DDoS mechanisms affecting email and web services in some instances, but did not experience them in our environment.

The tables below summarize results from the 2010 NAT444 testing at CableLabs, Time Warner Cable, and Rogers Communications. They are included for comparison with 2011 results, documented above.

Test Case Results Notes Web browsing pass Email pass FTP download pass performance degraded on very large downloads BitTorrent leeching pass BitTorrent seeding fail Video streaming pass Voice chat pass Netflix streaming pass Instant Messaging pass Ping pass Traceroute pass Remote desktop pass VPN pass Xbox Live pass Xbox online pass Blocked by some LSNs. Xbox network test fail Your NAT type is moderate. For best online experience you need an open NAT configuration. You should enable Universal Plug and Play (UPnP) on the router. Nintendo Wii pass behind one LSN, fail behind another PlayStation 3 pass Team Fortress 2 fail pass behind one LSN, but performance degraded StarCraft II pass World of Warcraft pass Call of Duty pass performance degraded behind one LSN SlingCatcher fail Netflix Party (Xbox) fail pass behind one LSN Hulu pass performance degraded behind one LSN AIM File Transfer pass performance degraded Webcam fail 6to4 fail Teredo fail

Test Case Results Notes BitTorrent leeching pass BitTorrent seeding fail Video streaming fail Voice chat pass Netflix streaming pass performance severely impacted, eventually failed IM pass Limewire leeching pass Limewire seeding fail

Test Case Results Notes Limewire leeching pass Limewire seeding fail uTorrent leeching pass uTorrent seeding fail

Test Case Results Notes Skype voice call pass IM pass FTP fail Facebook chat pass Skype video pass

Our testing did not focus on mitigating the impact of Carrier-Grade NAT, as described above. As such, mitigation is not the focus of this document. However, there are several approaches that could lessen the impacts described above. Challenge Potential Workaround(s) Peer-to-peer Use a proxy server; Gaming Negative impact to geolocation services Deploy CGN close to the edge of the network; use regional IP and port assignments Logging requirements for lawful intercept Deterministic Logging ; data compression ; bulk port logging Other mitigation techniques that are currently being researched, such as , may also improve performance.

Security considerations are described in and . In general, since a CGN device shares a single IPv4 address with multiple subscribers, CGN devices may provide an attractive target for Denial-of-Service attacks. In addition, as described in , abuse attribution is more challenging with CGN and requires content providers to log IP address, source port, and time to correlate with Service Provider CGN logs. Also, if a CGN public IP address is added to a blacklist (e.g., for SPAM) or if a server limits the number of connections per IP address, it could negatively impact legitimate users.

This document describes one of the network models that are designed for smooth transition to IPv6. It is called NAT444 model. NAT444 model is composed of IPv6, and IPv4 with Carrier Grade (CGN). NAT444 is the only scheme not to require replacing Customer Premises Equipment (CPE) even if IPv4 address exhausted. But it must be noted that NAT444 has serious restrictions i.e. it limits the number of sessions per CPE so that rich applications such as AJAX and RSS feed cannot work well. Therefore, IPv6 which is free from such a difficulty has to be introduced into the network at the same time. In other words, NAT444 is just a tool to make IPv6 transition easy to be swallowed. It is designed for the days IPv4 and IPv6 co-existence. &RFC3056; &RFC4380; In some instances, Service Providers have a legal logging requirement to be able to map a subscriber's inside address with the address used on the public Internet (e.g. for abuse response). Unfortunately, many Carrier Grade NAT logging solutions require active logging of dynamic translations. Carrier Grade NAT port assignments are often per-connection, but could optionally use port ranges. Research indicates that per-connection logging is not scalable in many residential broadband services. This document suggests a way to manage Carrier Grade NAT translations in such a way as to significantly reduce the amount of logging required while providing traceability for abuse response. While the authors acknowledge that IPv6 is a preferred solution, Carrier Grade NAT is a reality in many networks, and is needed in situations where either customer equipment or Internet content only supports IPv4; this approach should in no way slow the deployment of IPv6. NAT devices are required to log events like creation and deletion of translations and information about the resources it is managing. With the wide deployment of Carrier Grade NAT (CGN) devices, the logging of events have become very important for legal purposes. The logs are required in many cases to identify an attacker or a host that was used to launch malicious attacks and/or for various other purposes of accounting. Since there is no standard way of logging this information, different NAT devices behave differently and hence it is difficult to expect a consistent behavior. The lack of a consistent way makes it difficult to write the collector applications that would receive this data and process it to present useful information. This document describes the information that is required to be logged by the NAT devices. This memo describes a protocol for decentralizing IPv4 NAT to the customer-premises equipment (CPE) such that no state information is kept on the central NAT device. The CPE uses a restricted source port set that is encoded in its provisioned IPv4 WAN address. The NAT device performs only strictly stateless address (not port) translation.

Thanks to the following people for their testing, guidance, and feedback: Paul Eldridge Abishek Chandrasekaran Vivek Ganti Joey Padden Lane Johnson Also, thanks to Noel Chiappa for his comments.