# LTM L4 protocol profile explainer > The protocol-profile decision in cards: full-proxy tcp with every feature, the living f5-tcp-* four that F5 continually updates (read-only, tuned via child profiles) versus the frozen legacy -optimized trio, FastL4's PVA packet path with the loose pair for asymmetric routing, and FastHTTP's narrow-but-fast HTTP case with its complete when-to-use criteria list and K8024 as required reading. - Tool: https://ronutz.com/en/tools/f5-l4-profile-explainer - Family: Networking --- # LTM L4 protocol profile explainer Every BIG-IP LTM - Local Traffic Manager virtual server carries a protocol profile, and the choice among them is really three decisions wearing one dropdown. This tool renders the candidates as cards, each grounded in F5's own sources: the story, when to use it, the tradeoffs, and the details worth memorizing. The first decision is inside the full-proxy tcp family, and it is the living-versus-legacy split F5 announced with BIG-IP 13.0. The announcement's own words settle what the f5-* profiles are: f5-tcp-wan, f5-tcp-lan, and f5-tcp-mobile are updated versions of tcp-wan-optimized, tcp-lan-optimized, and tcp-mobile-optimized, adapting all settings to their link types without the very newest features, while f5-tcp-progressive is the general-use profile that carries the very latest features for early adopters. Those four, plus the default tcp, are living: F5 continually updates them with best practices, new features land in progressive immediately and in the conservative profiles a couple of releases later, and all five are read-only, so tuning means creating a child profile, where the custom flag pins any setting you never want a future update to touch. The legacy trio still ships, listed side by side with the living family in the current profiles reference, frozen for configurations that depend on exact values. The second decision is FastL4, and the card is honest that it is not a TCP proxy at all: the profiles reference states its purpose as letting the Packet Velocity ASIC hardware, where the platform supports it, process some or all of the Layer 4 traffic, paired with Performance (Layer 4) and Forwarding virtual servers. The operations guide supplies the when in one clause, little or no L4 or L7 processing required, and the tradeoff in another, minimal L7 information is available, so load-balancing decisions are limited in scope. The man page supplies the knobs: the pva-acceleration modes, the loose-initialization and loose-close pair for asymmetric paths (any-TCP-packet initiation and first-FIN close, both default disabled), timestamp and window-scale modes defaulting to preserve, and late-binding, where an iRule reads a FIX packet to pick the pool and hands the stream to ePVA hardware. The third is FastHTTP, defined by the reference as selected features of TCP Express, HTTP, and OneConnect combined into one profile, and qualified by a criteria list this card carries whole: no SSL traffic management, no compression, pipelining, or RAM Cache, no need to preserve source IPs, keep-alive-capable servers, and basic iRule support only, the reference's own examples being CLIENT_ACCEPTED, SERVER_CONNECTED, and HTTP_REQUEST. Read backwards, every criterion is a disqualifier, and the operations guide sends every deployment to K8024 first. Reference posture like its BIG-IP Zero Trust Access (formerly BIG-IP APM - Access Policy Manager) sibling: cards and lookup now, stanza parsing with a per-option audit as the documented roadmap. Everything runs locally. ## Standards and references - [F5 DevCentral: F5 Unveils New Built-In TCP Profiles (the 13.0 announcement, verbatim: f5-tcp-wan/lan/mobile as updated versions of the -optimized trio; f5-tcp-progressive as the general-use latest-features profile; the living contract, immediate landing in progressive and a couple of releases later elsewhere; the five read-only profiles and the child-profile custom-flag discipline; the benchmark criteria)](https://community.f5.com/kb/technicalarticles/f5-unveils-new-built-in-tcp-profiles/290729) - the living-vs-legacy story on the tcp-family cards - [BIG-IP LTM Profiles Reference 13.1 - Protocol Profiles (FastL4's purpose: PVA hardware processing some or all Layer 4 traffic, the virtual-server pairings, dynamic ePVA offload; FastHTTP's composition from TCP Express, HTTP, and OneConnect, its full when-to-use criteria list, and the Connection-header reuse benefit; the tcp-family descriptions and the mobile under-1-MB sizing note)](https://techdocs.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/ltm-profiles-reference-13-1-0/5.html) - the FastL4 and FastHTTP cards' stories and criteria - [BIG-IP LTM Profiles Reference 21.0 - Protocol Profiles (both TCP families, legacy and living, still shipping side by side)](https://techdocs.f5.com/en-us/bigip-21-0-0/big-ip-local-traffic-management-profiles-reference/protocol-profiles.html) - currency of the legacy trio - [tmsh ltm profile fastl4 man page v13 (option semantics with defaults: loose-initialization accepting any TCP packet rather than requiring a SYN and loose-close on the first FIN, both default disabled; pva-acceleration full/none/partial/dedicated; pva-offload-dynamic and -state; tcp-timestamp-mode and tcp-wscale-mode defaulting to preserve; mss-override; late-binding with the FIX-profile requirement)](https://clouddocs.f5.com/cli/tmsh-reference/v13/modules/ltm/ltm_profile_fastl4.html) - the FastL4 card's option quirks - [K93100324: BIG-IP LTM operations guide, virtual servers chapter (Performance (Layer 4) recommended when little or no L4/L7 processing is required, minimal L7 information limiting load-balancing scope, ePVA offload; Performance (HTTP) with FastHTTP, possibly the fastest way under certain circumstances with specific requirements and limitations, K8024 as required reading; Forwarding (IP) needing FastL4 options; translation disabled when steering to inspection devices)](https://my.f5.com/manage/s/article/K93100324) - the when-clauses and virtual-server pairings on both accelerated cards - [K8024: Overview of the Fast HTTP profile (the canonical requirements-and-limitations K article the operations guide points to; cited by number, my.f5 renders client-side)](https://my.f5.com/manage/s/article/K8024) - named as required pre-deployment reading on the FastHTTP card - [K09948701: Overview of the FastL4 profile (the canonical FastL4 overview K article; cited by number, my.f5 renders client-side)](https://my.f5.com/manage/s/article/K09948701) - companion overview for the FastL4 card ## Related reading - [Protocol Profiles: Living TCP, Frozen TCP, and the Two Fast Paths](https://ronutz.com/en/learn/bigip-l4-protocol-profiles.md): The tcp dropdown hides three decisions. F5's 13.0 announcement split the full-proxy family into living profiles it continually updates (read-only, tuned via children) and a frozen legacy trio that still ships. FastL4 trades the proxy for a hardware packet path, and FastHTTP is the narrow HTTP case that must clear every criterion on its list.