### Description [rfc5952#section-4.3](https://tools.ietf.org/html/rfc5952#section-4.3)

**4.3. Lowercase**

The characters "a", "b", "c", "d", "e", and "f" in an IPv6 address MUST be represented in lowercase.

### Expected behavior According to RFC

#### Actual observed behavior IPv6 addresses the upper case.

#### Debugging Data None

#### Log Messages None

#### SIP Traffic

``` OPTIONS sip:proxy.example.com;transport=tcp SIP/2.0 Via: SIP/2.0/TCP [2600:1F1C:257:8706:C6BA:A565:1E85:B29E];branch=z9hG4bKa3e9.cac3f2f1000000000000000000000000.0 To: sip:proxy.example.com;transport=tcp From: sip:proxy@example.com;tag=897804205b5fb4c6a22d7dcb9cb796fb-733ff025 CSeq: 10 OPTIONS Call-ID: 29ea7b443fbf87f8-2892@172.22.6.119 Max-Forwards: 70 Content-Length: 0 User-Agent: Kamailio ```

### Possible Solutions

Not known

### Additional Information

* **Kamailio Version** - output of `kamailio -v`

``` [centos@ip-172-22-6-226 ~]$ kamailio -v version: kamailio 5.5.0-dev2 (x86_64/linux) 60f04b flags: USE_TCP, USE_TLS, USE_SCTP, TLS_HOOKS, USE_RAW_SOCKS, DISABLE_NAGLE, USE_MCAST, DNS_IP_HACK, SHM_MMAP, PKG_MALLOC, Q_MALLOC, F_MALLOC, TLSF_MALLOC, DBG_SR_MEMORY, USE_FUTEX, FAST_LOCK-ADAPTIVE_WAIT, USE_DNS_CACHE, USE_DNS_FAILOVER, USE_NAPTR, USE_DST_BLACKLIST, HAVE_RESOLV_RES, TLS_PTHREAD_MUTEX_SHARED ADAPTIVE_WAIT_LOOPS 1024, MAX_RECV_BUFFER_SIZE 262144, MAX_URI_SIZE 1024, BUF_SIZE 65535, DEFAULT PKG_SIZE 8MB poll method support: poll, epoll_lt, epoll_et, sigio_rt, select. id: 60f04b compiled on 04:01:18 Sep 26 2020 with gcc 8.3.1 ```

* **Operating System**:

``` [centos@ip-172-22-6-226 ~]$ cat /etc/os-release NAME="CentOS Linux" VERSION="8 (Core)" ID="centos" ID_LIKE="rhel fedora" VERSION_ID="8" PLATFORM_ID="platform:el8" PRETTY_NAME="CentOS Linux 8 (Core)" ANSI_COLOR="0;31" CPE_NAME="cpe:/o:centos:centos:8" HOME_URL="https://www.centos.org/" BUG_REPORT_URL="https://bugs.centos.org/"

CENTOS_MANTISBT_PROJECT="CentOS-8" CENTOS_MANTISBT_PROJECT_VERSION="8" REDHAT_SUPPORT_PRODUCT="centos" REDHAT_SUPPORT_PRODUCT_VERSION="8" ```